I've done this today, but now cannot tighten/tension the cursed thing!
Take off top by removing screws; take off bottom (needed to break off plastic feet with a screwdriver) by removing small bolt-headed screws; removing two more bolt-headed screws, top and bottom allows casing to split in 2 halves at the sides, allowing you to slide on the new belt at the front. Simply put everything back together- and then please tell me how to tension it!
Brum Taffy, March 2008