Please note that in order to be able to edit a user other than your own profile, you must be a System Administrator.
To access the user administration click on your 'Settings' menu.
Go to the 'User Management' menu.
Click on the little pencil icon beside the user you would like to edit.
A dialog box will pop up with the chosen user's profile card. You will be able to edit the following fields:
First Name
Last Name
Email Alias
Roles (see this page for definition of each role)
Home Org Unit
Additional Org Units
Once you have made the desired changes, click the 'Save' button at the bottom of the box.