Open the hood of your Altima and locate the negative battery terminal on the battery. Loosen the retaining bolt on the negative battery cable end connected to the battery with a wrench or socket and ratchet. Lift the cable off the battery and isolate it from the terminals.
Place a jack under the passenger's side front suspension and lift the car off the ground. Support the car with a jack stand under the frame rail and remove the jack.
Locate the under body cover on the passenger's side of the car. Remove the mounting bolts that secure it to the car with a socket and ratchet then lower the cover down and move it out of the way.
Insert a long-handled breaker bar and socket into the engine compartment from under the car. Place the socket on the bolt in the center of the tensioner's idler pulley. Rotate the breaker bar toward the rear of the car, loosening the belt as the tension is relieved from the tensioner. You can now remove the belt if you need to or perform whatever work is required.The 2000 Nissan Altima uses a nylon-reinforced rubber serpentine belt to turn the accessories on the front of the engine. While these belts are durable, they do wear and stretch with use. The Altima uses a dynamic belt tensioner to tighten the belt and it adjusts to the belt as it wears. You can access the belt tensioner from under the car; you will need to have a long-handled breaker bar to reach it.