Ya know, its kinda tough at first, especially with wet hands...
You need to grip the front side of it, and pull it up first. By side, I am refering to the sides parallel to the rear wall. Once this is in there diagonally, you can lift it out with an easy wiggle. It will not lift straight up. Easiest place to grab it is in that goofy rectangle shape in the middle. Just pinch one end of it and lift.
Hope this helps !!