How do you replace a serpentine belt on a 2002 Ford E350 van?

To replace the serpentine belt on a 2002 Ford E350 van, first, locate the belt routing diagram, usually found under the hood. Use a wrench or a serpentine belt tool to relieve tension on the tensioner pulley, then slide the old belt off. Position the new belt according to the routing diagram, ensuring it's seated properly on all pulleys. Finally, release the tensioner to secure the belt in place and double-check the alignment before starting the engine.