With the sander unplugged, grasp the sander in both hands, right hand on handle with trigger, left hand on front handle. Place the front idler of the sander against your workbench and give it a forceful push. The pulley will latch about 3/8" back, releasing the tension on the belt. Lay the sander on its side and remove the used belt, install the new belt. Now with a flat screw driver locate the back oo the idler pully housing, (look for a somewhat flat piece that extends into the housing behind the name plate), place the tip of the screwdriver against that housing and push the idller pulley forward. This will release the catch that holds the pulley back so you can change the belt. There will be an audible "snap" when the idler pulley makes contact with the belt. Plug in the sander and run it with the belt facing up. On the oposite side of the sander from the belt is a knob about 3/4" in diameter, turning this knob will adjust the tracking of the belt, center the belt on the solid plate. There is NO tension adjustment, it is automatically controlled by the idler pulley latching mechanism.