You'll have to wait till all accounts are moved to the new free server, and you'll be able to change it yourself at: http://forums.x10hosting.com/account.php?action=modify.
Or maybe an Account Manager can help you, but I'm not really sure about this.
Yes once we have finish transfering account you will be able to change your domain, if you still can't do on your own at that time please post again asking for help.