our cars are like cheap snap together models. grab a corner/seam thats showing, and pull up on it. you'll hear it pop free. slide your hands down further and pull again.
eventually, you'll reach a spot where the other side will come free. WHA LA! you've removed a piece.
the back panels are more of a pain then the ones under the doors. but repeat the same steps. everything is snapped into place, so it just unsnaps when pulled on.
although AVOID pulling it at a weird angle. (don't like.. grab the panel under the door, and just try yanking the whole thing out from one end. when you hear one clip pop free, move down to get the next, don't keep pulling from the front. plastic breaks at sharp angles)