Lift the mower blade into the upright position via the lift bar and lock it in place just as you would do when storing the mower. This creates a straight line between all of the pulleys that control the mower deck drive system.
Remove the sheet metal screws that secure the belt guards over the belt system in the center of the mowing deck. Use a screwdriver to remove them and then place the covers off to the side.
Locate the idler pulley mounting bracket. It is the only pulley with a spring attached. Push the pulley away from the belt and then slip the belt over the pulley to release tension on the belt.
Remove the belt from the pulleys on the mower deck and then place the new belt onto the deck.
Push in on the idler pulley and then place the belt around the pulley. Let go of the idler pulley to lock the belt in place.
Place the covers onto the deck and secure them with the sheet metal screws and the screwdriver.