Unlike replacing a timing belt, the serpentine belt is far easier to replace at home, if you need to. The first thing you should do is disconnect your car's battery, just in case. Once that's been done, locate the serpentine belt on the front of the engine. Then, find the tensioner pulley and use a wrench to relieve tension on the belt. This will allow you to more easily slide the belt off of the pulleys. With the old serpentine belt removed, route the new one through those pulleys. Be mindful of how the belt had been routed originally, and how it looped or crisscrossed the numerous pulleys. Each engine should have a belt routing diagram that you can refer to. Finally, use the tensioner to apply some tension to the serpentine belt until its properly taut.