Well even if you did get on the wrong train, which I really doubt you will, just make sure to get on the one marked all terminals, they don't go all the way into the city, you take a five or ten minute ride, and it comes right back to the terminals. But that won't happen.

They are very easy to get to, and transferring with it is easier then many other airport transfers. Without luggage to worry about, you should have no problem at all.