You turn the bolt in the middle of the tensioner pulley to release the tension. You will be holding force against the spring force of the tensioner when you rotate it inwards. When you release the tensioner will go back into place until it hits its limit of travel since it will have no belt to pull against.

Think of the tensioner as a pulley on a spring. All you are doing by releaseing the tenioner is moving the pulley against a spring to provide enough clearance to get the belt off. The pulley naturally returns to its original state when you release the force on it. Just put a socket on the pulley and you will understand.

All you need is a 15mm (I think) socket and a new belt, and maybe a diagram of how the belt is routed in case you forget. You can find a diagram in the owner's manual.

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record