When you set up Ubuntu, it automatically adds the first user to the sudo group, allowing that user to make changes as the super user (root) by typing in their password. However, it doesn’t automatically add additional users to the sudo group. If you want to give someone else superuser privileges on your shared system, you’ll have to give them sudo access.
To add new users to sudo, the easiest way is to use the usermod command.
sudo usermod -G admin username .
That’s all there is to it.
However, if the user is already a member of other groups, you’ll want to add the
-a option, like so:
sudo usermod -a -G admin username .
If you prefer the GUI way of doing things, go to System -> Administration -> Users and Groups. Select the user you want to add to sudo, and click Properties. Under the User privileges tab, check the box that says “Executing system administration tasks” and you’ll be all set.