Using a socket and ratchet or tensioner pulley tool, rotate the the tensioner pulley and slip off the belt. Inspect all the pulleys and make sure they are clean and not damaged.
To install a new belt simply route the belt around all the pulleys according to the diagram above leaving the tensioner pulley for last. Check all the pulleys again to make sure the belt is on all of them correctly and rotate the tensioner pulley and slide on the belt.
Inspect the belt and make sure it is on every pulley correctly before starting your vehicle. Adjustments are made by simply rotating the tensioner pulley just enough to give the belt some slack and slide into position.