the shelf is just cardboard.
if you were trying to pull a bent nail from a loose 2x4 .. would you just edge the hammer in and pry up ? no .. you would step on the board to stop it from flying up into the air as you pry.
so rule #1: hold the rest of the enclosure down while you try to pull up the grill on the other side.
if you used any kind of pry-bar on the small grills you are trying to pull off, you would severly damage them and the enclosure they are in. grab a flathead from a eye glasses repair kit. stick it inbetween 1 of the million holes in the grills and pill up (don't forget about rule #1).
like i said before .. the grills are not fastened on by ANYTHING. they are literally just held in by a very thin and easily torn rubber piece. they are pushed in by hand. they are not welded on by a skilled craftsman or held in there by anything. i've removed ones that were "stuck" and "hard" (using the word hard VERY loosely) to get out. they still come out without issues.