NOTE: You cannot change the home department of the Administrator user.
In Content Administration:
Click the Users entry under any department to which the user is assigned.
Click the Edit Departments button.
Click the Home department drop-down list.
Select a different department.
If you do not want the user to remain a member of the previous home department, de-select it in the list at the bottom of the dialog.
Click OK.
Click the Save the changes made to this entry icon in the toolbar.