If you're going to remove major pieces of interior trim, it's best to heat the interior of the truck first; this makes the plastic soften slightly and will help prevent possible breakage.
Many of the attaching screws and pins are hidden by plugs, caps, etc. or are the attaching point for clips or brackets. The plugs and caps can be removed with light prying action. Don't force anything–if the trim isn't coming out, it's because you've missed a screw or clip somewhere. Most attaching hardware is located around the perimeter or near the center of the piece. Don't forget to reinstall the ornamental plug or cap that hides the screw when the part is back in place.
Also, some moldings cannot be removed without first removing the adjacent molding. It may seem like more work than necessary, but if you force something that isn't meant to come out yet, something is bound to break.