Make an existing user part of Administrators

[Gianluca Cecchi]

Hello,
during install of F17 and F18 you are required to create a user.
Also, you can flag if you want to make it part of administrator group.

What is the command that runs under the scenes?
What are the GUI steps to reproduce the same effects for an existing
user after install?

perhaps:
- uncomment the %wheel line in sudoers
- make the user part of wheel group
?

thanks in advance

gianluca