Remove the Glove box by pulling the 2 knobs of each side of the box. Let it hang. You will be looking at the filter, pull it out and replace it.
If your not mechanically inclined, buy the video on how to Fix Your Lexus, I did...saved me thousands on repairs. Now I know why they say taking it to a dealer is a rip off. Here's a link to the video, http://www.youtube.com/watch?v=Fmo-WcinNhU
At the end of the video is an email address. Ask him for the video. Hope this was helpful.