The early registration/reservation for Clan names has ended. When it started on October 14, 2013, Clan Leaders got the information about this on their Clan's Elite page. From there they were able to reserve a name or create a new name for Ghosts as well as copy their Clan Roster over or not. As LifeSong1 stated, you will just have to wait until November 5th, 2013 to be able to reuse your Clan name or create a new one. With Cross Platform now in effect for Clans, it is first come-first serve for Clan names. If someone has already used your current Clan name for a Ghost Clan name, you wouldn't be able to use it anymore. You'll have to create a new one.