I have deleted my main account and can't update or authenticate any change I want to make.

When you turn on the computer, hold down SHIFT until the GRUB menu appears.

Use the up and down arrows to select the first entry that has (recovery mode) at the end, e.g.:
Ubuntu, Linux 2.6.32-24-generic (recovery mode)
and press ENTER.

You'll soon get a blue screen with a grey Recovery Menu on it. From it, pick:
root Drop to a root shell prompt

At the bottom of the screen, a command prompt will appear.

If you've already created a user account for yourself, skip to the next paragraph; if not, enter:
adduser rudsel (or whatever you want your username to be)
Enter the password you'd like at the two prompts.
Enter your full name when prompted; the subsequent details are optional.
If you've entered everything correctly enter y when asked if everything is correct.

To make yourself an administrator, at the command prompt, type:
usermod -a -G adm,dialout,cdrom,plugdev,lpadmin,admin,sambashare rudsel
Obviously, this assumes a username of "rudsel"; change if necessary.

You can check you've been added to all the groups, by typing:
groups rudsel

When happy that you're now an admin, type:
shutdown -r now
to restart.
You should now be able to make all the changes you want.