I removed one once by using the rounded end of an old school can opener, not the pointed end. Gently start at the base of the front (windshield) and pry up from the bottom then down from the top side just to loosen it. Do this every couple of inches until you get to the seam at the door pillar (center post).
If you're lucky it might start to pop off and allow you to slide it on the gutter itself. One time I took a piece of wood and tapped from the bottom with a hammer to help loosen it. I hope this makes some sense.

Thanks.