Spray WD40 on the grommets. Theres 4 grommets, 2 on the bottom and 2 on the side. I found out it was either to pull the ones out of the side then pull up. Just keep wriggling it back and forth and it will slowly come out.
WD40 or similar is your best friend.......pull your filter out, spray wd on the bottom rubber from inside the box, and pull up....usually the fender ones would just pop out for me after the bottom is popped off.