1999 Nissan Maxima Cabin filter replacement

I have recently tried to replace cabin filter with no success. I have glove box off and could swear I have all the screws out and clip off , but can only get bottom to move down about an inch . Can see filter and its very dirty don't think it has every been changed.Can you please help and let me know what I am doing wrong . Is there another screw I can't see or a clip under the hood . I can get whole case to move but can't get it to open . Thanks for any help