They should have a flush appearance when seated normally. The centre will push in, probably about 1/8" allowing them to release. These can require firm pressure, especially if they've never been removed before. The entire rivet can then be removed. It'* probably easier to gently pull down on the trim to pop them out rather than to try and pry them out. Once out, they can be reset for installation when your're done. The centre should be positioned so that it sticks out. Once placed in the hole, press the centre in until they are flush.
StingRay Bike w/cards in the spokes, Weeeeeee!