Windtunnel belt

You didn't state your model number, they have different ones. Take off the bottom plate, the belt and brushroll will be exposed. If you canned see the motor shaft to put the belt on, then the top cover will have to removed also. Usually is a couple of screws from the bottom to take out, then you wil see a slot on each side from the bottom, use a flat blade screwdriver, put intoi slot and pry up to release locking tabs, top will come off. Belt goes from brush roll to motor shaft. If this is the model that uses 2 belts, then the belt goes from the motor shaft to the bigger pulley, and the Vee belt goes from the smalled pulley to the brush roll.