They come out. I took the center one out to see my 5th wheel better and it helps a lot. I also took the center head rest out of the front seat (if you have the 40/20/40 seat) and that really changed the look of the truck.
At the base of each leg, there is a little square plastic piece that is part of the seat back. The leg of the head rest goes down inside this piece. On the side of this square piece there is a tab that you push in and slide the head rest up and out as you hold them. The trick is to press both tabs and cup your hand to push up all at the same time. Or get someone to help. They slide easy or hard, depending on the fit, but they will come out.