If its your first time it'll take you around 30 minutes. Its easy.
Once you've opened the machine up, Unscrew the two black wires (might be a black and a white wire but don't worry to much which order you put them in)
Unscrew the earth cable.
Then remove the three bolts holding the vac motor. Stick on new rubber gasket on new vac motor and bolt the new vac motor in place. (not too tight! You want the vac motor to be secure but don't over tighten). Screw in the two wires back in to the white thing. Screw the earth cable back in. And your done.
When you open up the machine remember to lift the catch holding the exhaust pipes to the side of the machine.
Thats all, three wires and three bolts.
So, you'll need a screw driver. And a small spanner.