I can't install mavl.dm package of mcafee antivirus due to popup saying less space in /home/user.what to do for this problem

What is the output of:

lsb_release -a; uname -a; df -h

Thanks

output of lsb_release -a
distributer id:ubuntu
description:ubuntu 16.04.4 LTS
release: xenial
output of uname -a:
Linux mritunjay-Inspiron-5567 4.4.0-130-generic #156-Ubuntu SMP Thu Jun 14 08:53:28 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
output of df -h:
Filesystem Size Used Avail Use% Mounted on
udev 1.9G 0 1.9G 0% /dev
tmpfs 386M 6.3M 379M 2% /run
/dev/sda3 904G 6.9G 851G 1% /
tmpfs 1.9G 7.2M 1.9G 1% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
/dev/loop0 87M 87M 0 100% /snap/core/4830
/dev/loop1 87M 87M 0 100% /snap/core/4917
/dev/sda1 596M 24M 573M 4% /boot/efi
tmpfs 386M 72K 385M 1% /run/user/1001
/home/mritunjay/.Private 904G 6.9G 851G 1% /home/mritunjay

Available disk space in /home/mritunjay is too low. Minimum of 610 MB is required.

this is popup message when i click install on mavl.dm package of mcafee antivirus

Are you running an email server or a file server with Windows clients? If not then you really don't need antivirus. Is this a production server in a business?

https://www.howtogeek.com/135392/htg-explains-why-you-dont-need-an-antivirus-on-linux-and-when-you-do/

it's ok , but can you tell why is this happening... because in df -h command the size of filesystem /home/mritunjay/.private is 904 gb and used is 6.9g then where is rest. Also, how can i check disk space of /home/mritunjay as df -h shows space of /home/mritunjay
thanks.