This post to give you some tips for Team Foundation server,i will answer for some FAQ related to TFS ?
1) Can I Upgrade from TFS workgroup edition to TFS ?
YES YOU CAN,BELOW LINK TELLS YOU HOW TO DO THAT.
2) Can I Make My TFS Installation Licensed even after the Trial Version expired ?
YES,YOU CAN,GET YOUR KEY,REPAIR TFS and put the Licensed KEY.
3) Can I extend the trial period for my Trial TFS Installation ?
YES,YOU CAN,BELOW LINK SHOWS HOW TO DO THAT.
HOPE THIS HELPS :)