Unplug the washing machine and close the water valves leading to the washer.
Disconnect the water hoses from the wall and slide the washing machine away from the wall.
Unscrew the four screws securing the back access panel. There will be one in each corner of the panel. Pull the panel up and out.
Locate the belt and the two clamps holding the belt in place.
Unscrew the clamps until the belt is loose enough to remove.
Pull off the old belt and put the new belt on.
Tighten the clamps until they are firmly holding the new belt in place.
Replace the back panel, slide the washing machine back in place, connect the water hoses, plug the washing machine in and turn the water supply back on.