Removing the panels: there's usually a few screws, hidden in handle-wells or other depressions. Then, just pull straight out around the edges of the panel - there are plastic clips on the panel that go into metal clips on the van, they're pretty hard to pull out so you have to give them some force. The window surrounds I'm pretty sure have no screws, just the clips.
On the side, bottom panels, they lift up and then out, once the screws are removed. The clips are different and are more hook-like, I seem to recall.
Sorry I can't be more specific, it's been a while