the belt should run around two (or more ) wheels, @ least one of these should be mounted with screws or bolts that press something that looks like a track in a set position. loosen these screws/bolts, push the wheels closer together, this should allow the belt to fit over the wheels, push the wheels apart until yhe new belt is taught and tighten the screws/bolts. the belt should have about a quarter inch movement when pressed in the middle of the longest streach, if u over tighten the belt may snap, too louse and it comes off.
all the best
gary mc, February 2005