The old Gnome 2 User and Groups management tool has been turned off since Ubuntu 11.10 Oneiric. But it’s still avaiable in Ubuntu repository contained by package gnome-system-tools.

So if you’re looking for this easy to use graphical method for modifying users’ group membership in Ubuntu 12.04, use following method to get it back.

In Ubuntu Software Center search and install gnome-system-tools, then you can launch Users and Groups in the Dash.

Or install it via apt-get command:

sudo apt-get install gnome-system-tools

Now, you get back this old Users Settings tool:

easily edit user advance settings:

manager groups: