sudo apt-get update is not working

For diagnostic purposes please provide the full output that you receive for the commands

uname -a
lsb_release -crid
sudo apt update

query ) uname -a
Linux shaifali-hp-notebook 4.15.0-88-generic #88~16.04.1-Ubuntu SMP Wed Feb 12 04:19:15 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

query ) lsb_release -crid
Distributor ID: Ubuntu
Description: Ubuntu 16.04.3 LTS
Release: 16.04
Codename: xenial

query 3) sudo apt update

Hit:1 http://in.archive.ubuntu.com/ubuntu xenial InRelease
Get:2 http://in.archive.ubuntu.com/ubuntu xenial-updates InRelease [109 kB]
Get:3 http://in.archive.ubuntu.com/ubuntu xenial-backports InRelease [107 kB]
Get:4 http://security.ubuntu.com/ubuntu xenial-security InRelease [109 kB]
Hit:5 http://archive.canonical.com xenial InRelease
Hit:6 http://ppa.launchpad.net/alexlarsson/flatpak/ubuntu xenial InRelease
Ign:7 http://old-releases.ubuntu.com/ubuntu raring InRelease
Hit:8 http://ppa.launchpad.net/gezakovacs/ppa/ubuntu xenial InRelease
Get:10 http://in.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages [2,049 kB]
Hit:11 http://ppa.launchpad.net/inameiname/stable/ubuntu xenial InRelease
Get:9 http://old-releases.ubuntu.com/ubuntu raring Release [40.8 kB]
Get:12 http://in.archive.ubuntu.com/ubuntu xenial-updates/main i386 Packages [1,525 kB]
Get:13 http://in.archive.ubuntu.com/ubuntu xenial-updates/main amd64 DEP-11 Metadata [327 kB]
Get:14 http://in.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 DEP-11 Metadata [281 kB]
Ign:15 http://in.archive.ubuntu.com/ubuntu xenial-updates/multiverse amd64 DEP-11 Metadata
Ign:16 http://in.archive.ubuntu.com/ubuntu xenial-backports/main amd64 DEP-11 Metadata
Hit:17 http://ppa.launchpad.net/jonathonf/ffmpeg-4/ubuntu xenial InRelease
Ign:18 http://in.archive.ubuntu.com/ubuntu xenial-backports/universe amd64 DEP-11 Metadata
Ign:15 http://in.archive.ubuntu.com/ubuntu xenial-updates/multiverse amd64 DEP-11 Metadata
Ign:16 http://in.archive.ubuntu.com/ubuntu xenial-backports/main amd64 DEP-11 Metadata
Ign:18 http://in.archive.ubuntu.com/ubuntu xenial-backports/universe amd64 DEP-11 Metadata
Get:19 http://old-releases.ubuntu.com/ubuntu raring Release.gpg [933 B]
Get:15 http://in.archive.ubuntu.com/ubuntu xenial-updates/multiverse amd64 DEP-11 Metadata [6,426 B]
Ign:20 http://ppa.launchpad.net/kazam-team/stable-series/ubuntu xenial InRelease
Hit:21 http://dl.google.com/linux/chrome/deb stable InRelease
Get:16 http://in.archive.ubuntu.com/ubuntu xenial-backports/main amd64 DEP-11 Metadata [3,490 B]
Get:18 http://in.archive.ubuntu.com/ubuntu xenial-backports/universe amd64 DEP-11 Metadata [7,090 B]
Hit:22 http://ppa.launchpad.net/maarten-baert/simplescreenrecorder/ubuntu xenial InRelease
Hit:23 http://ppa.launchpad.net/morphis/anbox-support/ubuntu xenial InRelease
Hit:24 http://ppa.launchpad.net/otto-kesselgulasch/gimp/ubuntu xenial InRelease
Ign:25 http://ppa.launchpad.net/sicklylife/gnucash/ubuntu xenial InRelease
Hit:26 http://ppa.launchpad.net/sylvain-pineau/kazam/ubuntu xenial InRelease
Err:27 http://ppa.launchpad.net/kazam-team/stable-series/ubuntu xenial Release
  404 Not Found
Err:28 http://ppa.launchpad.net/sicklylife/gnucash/ubuntu xenial Release
  404 Not Found
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/kazam-team/stable-series/ubuntu xenial Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://ppa.launchpad.net/sicklylife/gnucash/ubuntu xenial Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

In your package management configuration you have references to two PPAs which do not contains software for Ubuntu xenial.
Remove the entries, and the error messages will disappear.

For identifying the details please provide the output of the command

find /etc/apt -name '*.list' -exec bash -c 'echo -e "\n$1\n"; cat -n "$1"' _ '{}' \;

Remarks:
1. also the entry for "old-releases - raring" should be removed, because it is obsolete.
2. Support for Ubuntu xenial has already ended (is now in ESM status), so you should plan an upgrade to a supported release in due course. see https://wiki.ubuntu.com/Releases

query ) find /etc/apt -name '*.list' -exec bash -c 'echo -e "\n$1\n"; cat -n "$1"' _ '{}' \;

/etc/apt/sources.list.d/alexlarsson-ubuntu-flatpak-xenial.list

     1 deb http://ppa.launchpad.net/alexlarsson/flatpak/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/alexlarsson/flatpak/ubuntu xenial main
     3 # deb-src http://ppa.launchpad.net/alexlarsson/flatpak/ubuntu xenial main
     4 # deb-src http://ppa.launchpad.net/alexlarsson/flatpak/ubuntu xenial main

/etc/apt/sources.list.d/morphis-ubuntu-anbox-support-xenial.list

     1 deb http://ppa.launchpad.net/morphis/anbox-support/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/morphis/anbox-support/ubuntu xenial main

/etc/apt/sources.list.d/otto-kesselgulasch-ubuntu-gimp-xenial.list

     1 deb http://ppa.launchpad.net/otto-kesselgulasch/gimp/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/otto-kesselgulasch/gimp/ubuntu xenial main

/etc/apt/sources.list.d/kazam-team-ubuntu-stable-series-xenial.list

     1 deb http://ppa.launchpad.net/kazam-team/stable-series/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/kazam-team/stable-series/ubuntu xenial main
     3 # deb-src http://ppa.launchpad.net/kazam-team/stable-series/ubuntu xenial main

/etc/apt/sources.list.d/google-chrome.list

     1 ### THIS FILE IS AUTOMATICALLY CONFIGURED ###
     2 # You may comment out this entry, but any other modifications may be lost.
     3 deb [arch=amd64] http://dl.google.com/linux/chrome/deb/ stable main

/etc/apt/sources.list.d/sylvain-pineau-ubuntu-kazam-xenial.list

     1 deb http://ppa.launchpad.net/sylvain-pineau/kazam/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/sylvain-pineau/kazam/ubuntu xenial main

/etc/apt/sources.list.d/inameiname-ubuntu-stable-xenial.list

     1 deb http://ppa.launchpad.net/inameiname/stable/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/inameiname/stable/ubuntu xenial main

/etc/apt/sources.list.d/ia32-libs-raring.list

     1 deb http://old-releases.ubuntu.com/ubuntu/ raring main restricted universe multiverse

/etc/apt/sources.list.d/gezakovacs-ubuntu-ppa-xenial.list

     1 deb http://ppa.launchpad.net/gezakovacs/ppa/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/gezakovacs/ppa/ubuntu xenial main

/etc/apt/sources.list.d/sicklylife-ubuntu-gnucash-xenial.list

     1 deb http://ppa.launchpad.net/sicklylife/gnucash/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/sicklylife/gnucash/ubuntu xenial main
     3 # deb-src http://ppa.launchpad.net/sicklylife/gnucash/ubuntu xenial main

/etc/apt/sources.list.d/jonathonf-ubuntu-ffmpeg-4-xenial.list

     1 deb http://ppa.launchpad.net/jonathonf/ffmpeg-4/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/jonathonf/ffmpeg-4/ubuntu xenial main

/etc/apt/sources.list.d/maarten-baert-ubuntu-simplescreenrecorder-xenial.list

     1 deb http://ppa.launchpad.net/maarten-baert/simplescreenrecorder/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/maarten-baert/simplescreenrecorder/ubuntu xenial main

/etc/apt/sources.list

     1 # deb cdrom:[Ubuntu 16.04.3 LTS _Xenial Xerus_ - Release amd64 (20170801)]/ xenial main restricted
     2
     3 # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
     4 # newer versions of the distribution.
     5 deb http://in.archive.ubuntu.com/ubuntu/ xenial main restricted
     6 # deb-src http://in.archive.ubuntu.com/ubuntu/ xenial main restricted
     7
     8 ## Major bug fix updates produced after the final release of the
     9 ## distribution.
    10 deb http://in.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
    11 # deb-src http://in.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
    12
    13 ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
    14 ## team. Also, please note that software in universe WILL NOT receive any
    15 ## review or updates from the Ubuntu security team.
    16 deb http://in.archive.ubuntu.com/ubuntu/ xenial universe
    17 # deb-src http://in.archive.ubuntu.com/ubuntu/ xenial universe
    18 deb http://in.archive.ubuntu.com/ubuntu/ xenial-updates universe
    19 # deb-src http://in.archive.ubuntu.com/ubuntu/ xenial-updates universe
    20
    21 ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
    22 ## team, and may not be under a free licence. Please satisfy yourself as to
    23 ## your rights to use the software. Also, please note that software in
    24 ## multiverse WILL NOT receive any review or updates from the Ubuntu
    25 ## security team.
    26 deb http://in.archive.ubuntu.com/ubuntu/ xenial multiverse
    27 # deb-src http://in.archive.ubuntu.com/ubuntu/ xenial multiverse
    28 deb http://in.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
    29 # deb-src http://in.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
    30
    31 ## N.B. software from this repository may not have been tested as
    32 ## extensively as that contained in the main release, although it includes
    33 ## newer versions of some applications which may provide useful features.
    34 ## Also, please note that software in backports WILL NOT receive any review
    35 ## or updates from the Ubuntu security team.
    36 deb http://in.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
    37 # deb-src http://in.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
    38
    39 ## Uncomment the following two lines to add software from Canonical's
    40 ## 'partner' repository.
    41 ## This software is not part of Ubuntu, but is offered by Canonical and the
    42 ## respective vendors as a service to Ubuntu users.
    43 # deb http://archive.canonical.com/ubuntu xenial partner
    44 # deb-src http://archive.canonical.com/ubuntu xenial partner
    45
    46 deb http://security.ubuntu.com/ubuntu xenial-security main restricted
    47 # deb-src http://security.ubuntu.com/ubuntu xenial-security main restricted
    48 deb http://security.ubuntu.com/ubuntu xenial-security universe
    49 # deb-src http://security.ubuntu.com/ubuntu xenial-security universe
    50 deb http://security.ubuntu.com/ubuntu xenial-security multiverse
    51 # deb-src http://security.ubuntu.com/ubuntu xenial-security multiverse
    52 deb http://archive.canonical.com/ xenial partner
    53 # deb-src http://archive.canonical.com/ xenial partner

Issue the following commands:

sudo rm /etc/apt/sources.list.d/ia32-libs-raring.list
sudo rm /etc/apt/sources.list.d/sicklylife-ubuntu-gnucash-xenial.list
sudo rm /etc/apt/sources.list.d/kazam-team-ubuntu-stable-series-xenial.list

Then try "sudo apt-get update" again, and I hope the errors are gone.

How to remove the entries for "old-releases - raring"

The command for removing the raring entry is the first one of the three commands in comment #5
The second and third are for the "404 not found" - "no release file" errors.

Thanks Manfred , you have solved both my problems . Thanks man