I was on it just a few days ago. There's nothing difficult about it...especially if you're headed from T2 to T4. If you were going the opposite direction (to T8), you would have to make sure you were on the terminal loop train. But any train going in your direction will take you where you need to be.

Oh, and that was my first time at JFK too, so it's not like I'm a local that knows all the ins and outs. It's easy...just follow the signs and hop the first train that comes through (heading in the right direction).