How do you use Server Admin to modify Network settings

Hello MAC World,

I am very new to Mac and I have been trying to change the workgroup on a Mac Mini. In System Preferences->Network->Advanced->Wins all the options are greyed out. On the bottom of the Network window it states "Use Server Admin to modify these settings". I have been all through Server Admin with no luck finding the workgroup setting. I have duplicated the Ethernet service but the workgroup options are still greyed with the same message. I have read post that suggested using Directory Access however this application cannot be found.