If you do manage to get the screw out on the back of the "L" bracket (back of the filter) I'd take it to your local hardware store and get one that has a HEX head, so you can just use an Allen wrench to get it out. It seems like Honda put Loc-Tite on that lil sucker which makes it difficult to get out. Also, I am assuming this is one of your first times changing the filter (sorry if I assume incorrectly), but while changing it you should clean your air box. Be sure to put a rag or something in your intake to be sure no dust or anything gets in there, and you can wipe your intake out as well, sometimes dirt and dust gets up in there.
2008 700xx; Power Bomb header with power core 4 exhaust, Power Programmer III, pro armor nerfs, prm products control front and rear bumpers and full skid, 10" ITP rears, ITP Baja's fronts, RZR 2's all the way around, Uni filter, 13t sprocket, CCP steering Damper, DS450 shock swap, Dual Gasser Throttle, bar risers and Moose barkBusters. 730XX kit plus other engine mods!