I've just called them and this helpful chap put me on hold and then came back and said basically they get a call (or official word direct to them) from Frank Warren (he said Frank Warren so he did some research) to confirm its moving to Manchester, then they send out an e-mail to everyone with tickets that gives you instructions on how to send the tickets back to get your money back. He said no to worry and just wait for the e-mail from them. To be fair thats exactly what Viagogo did with my Haye tickets, which surprised me as didn't expect to get a refund. Well pleased when I did though. I just replied to a mail via their site and they refunded it right away, I think this'll be the same with Ticketmaster.