Too much has changed, it is not an "upgrade to" UBB.7, its an "Import From 6.5"; it's an almost total rewrite, in fact, i'd be willing to say that any attempt to just "upgrade" will completely nerf your forums.
In a nuttshell, install UBB.T7 on your server in a seperate directory and go to the "Add Admin User" screen, then run the UBB.T7 Importer (from UBB.T); after the import is complete you can login to UBB.T7 and manage your newly imported forum.
