Disconnect the belt sander from the power outlet.
Place the belt sander on its left side. Lift the tension release lever found in the center of the right side, between the front and rear roller. Lifting this lever will release the tension on the sanding belt.
Pull the old sanding belt off the front and rear rollers.
Slide a new sanding belt of the same size onto the rollers. Adjust the position of the belt so that it is centered on the rollers and push the tension release lever back into position, tightening the tension on the belt.
Plug in the sander and turn the unit on. The belt should rotate centered on the front and back rollers. If the belt is out of position, turn the unit off, release the tension lever, adjust the belt and return the tension lever back into position.