To add or remove users from a workgroup requires that you be defined to that workgroup as an Assistant Manager.  This is the best way to handle this situation:  Ask the Workgroup manager to add you to that Workgroup as an Assistant Manager.  Portal Tools > Manage Workgroups > Workgroup Manager > then click the Padlock Icon for the Workgroup > Add\Remove (you or other user) > OK  --- Next the Workgroup Manager will find the added name in the listed Assistant Managers > Edit Permissions click the Lock by the name > Select All or choose the permissions to be given.  Click OK > Return to Workgroup Manager

The permissions given control the user's capabilities for that specific Workgroup.