the spin motor is, I believe, different on US models, but this is what we do on Australian models:

The spin motor mounts on a triangular plate that bolts to a cross member which also supports the bottom bearing of the spinner assembly.

Disconnect washer from power. (D'oh.)

Tip the machine upside down.

the cross member is a U-channel, now the machine is upside-down you can see the bolt heads that locate the spin motor (2 bolts) and the spinner bottom bearing/rubber resilient mount (2 bolts).

Slacken the spin motor bolts, but don't remove them - two bolts - and slide the motor a little towards the spinner, to slacken the belt.

Disengage the spinner belt from the spin motor. The belt is still trapped around the spinner pulley at this stage.

At this point you can now easily remove the elasticated pump belt and fit the new one.

Mark the cross member where the spinner bolts are located, so you will be able to refit the bolts in exactly the same position in the slots.

Now remove the bottom spin bearing bolts (As the machine is upside-down, they are at the top). You will now be able to slide the pulley (with bottom bearing and resilient rubber mount attached) away from the cross member, to create a gap where you can remove the spinner belt and fit the new belt.

You don't have to remove the spin pulley from the spin can, which is good as it can be a rotten job.

Once the belt is around the bottom spinner pulley, you can refit the bottom mount bolts, lining them up with the marks you made earlier. If the spin can sat crooked in the tub, you can adjust the bolts in the slots to get the spin can centered in the tub.

From here it is just reassembling what you disassembled.