Ive just replaced mine.
Remove the top (3 screws on the back).
Once inside disconnect the three wires Live Neut and earth.
Take all the screws out from the back panel (Outer edge only) and the whole back should pull out, drum included.
Slip belt round the drum so it sits at the back of the drum.
Replace the drum making sure the belt isnt caught.
Put all the screws back in the rear panel.
Pull the belt off the drum slighty so you can attach the belt round the motor pulley. With someone keeping the belt on the motor pulley, slowley rotate the drum whilst holding the belt on the drum and it should slip straight back on.
I found the otherway of forceing the belt over the pulley with a screw driver rather difficult, and not only that, you can damage the metal grooves on the pulley which will undoubtedly reduce the life of your new belt.
Paul, August 2009