You should replace your serpentine belt as often as it is needed. Recommended Manufacturer intervals ar every 15,000 miles for inspection and Every 45,000 for replacement. This is usually a fairly simple process as can be seen in the video to your right. Just make sure you study the position or draw a picture to help you remember how to put the new one back on. Release pressure from the belt tensioner and swap out the belt. Some variations may apply but it is basically the same process.