You can only move two in/out of the dock bar. You HAVE to keep the phone and app buttons. But the contact and messages and be swapped. Just go into the app drawer, long press the dock(if you want to remove one/swap. Or bring one in from the app drawer to the dock.
That or you can get FULL customization by downloading a launcher(which many people do). It is easy, quick and free. I have GO Launcher ex, there are others on the market.