Upvote:9
JFK has an AirTrain which runs every few minutes between all the terminals. This would be the fastest way to travel between them, you can also walk.
After going through customs/security (depending on where you have come from etc) you can go directly to the AirTrain. Ensure you go in the correct direction. Then just hop off at the correct stop! There's loads of signs around directing you to the trains, I found them very hard to miss.
You can find more details about the train here.