Click the "Domains" tab on the left hand side bar to open a drop down menu.

Press "List Domains" on the newly opened menu.

This brings you to a List of all domains you have administrative power over.

Next to each Domain name is a green box that says "Edit" in it, click this to open the edit menu for the desired domain.

This opens a screen where you can change passwords, grant and restrict services, or change the group assignment.