Check to make sure that your mower is turned off and is in the park position. As an extra safety measure, you may also unplug the battery cables and spark plug wires to make sure that the engine will not accidentally start.
Put the shift lever into the lowest position and remove the mower deck.
Unscrew the cap screws and belt shield from the drive belt with a screwdriver.
Loosen the sheaves around the drive belt.
Loosen the belt guides.
Disconnect the belt shield from the drive belt.
Use a clean, dry cloth to wipe the mower desk and sheaves.
Carefully inspect the old belt for wear. Remove the belt and attach the new one. Be sure to put the new belt securely into the grooves of the belt guides and the grooves in each sheave to prevent it from slipping out.
Tighten the sheaves back around the drive belt area. Re-mount the belt shield and mower deck.