Take off the blade, the fan and the small grey, circular, plastic cover.
On the same side (the underside), remove all the screws - If I remember correctly, there are 8 in total.
On the top side, there are two screws securing the orange plastic motor cover at the front. Remove these as well.
You should now be able to withdraw the belt/motor/spindle assembly from the inside of the machine.
Look at the underside of the assembly at the motor end: There are four screws in a square arrangment, through elongated holes. You need to loosen these to enable you to slide the motor assembly back in order to let you get the belt over the motor and blade spindles.
Alternatively, leave these four screws alone and you might be able to get the new belt on, albeit with quite a bit of effort.
Use your own discretion. If you opted for the former approach there, you now need to tension the belt and retighten those four screws.
As for the rest of it... Refitting is the reverse of removal.
R Glass, June 2004