The cabin air filter is behind the glove box, you need to pull the side stick that hangs out on the right hand corner and apply pressure until the whole thing eventually drops.....I have an Acura TSX as well as a Lexus IS350, the Acura is almost similar to the Lexus but the Toyota/Lexus theirs require alot of force. I've heard people complain about their glove box breaking easily, be careful.
Air filter is under the hood....
http://www.knfilters.com/images/press/cam1.jpg
look at this photo, there should be a box covering the whole thing. open that and swap the filter