Ensure that the mower is first parked securely on a flat stable surface – turn off the engine and wait for all moving parts to come to a complete stop before you proceed. Identify the idler pulley and gently work the belt off the pulley shaft and mandrels. Pull the pulley out of the unit and replace with the new belt. Force the belt through the mandrels and then work it around the idler pulleys. Check that the belt is sitting snugly in within all the necessary grooves.