As Saj has said the whole glovebox needs to be removed and from memory there is a metal brace bar that you either remove on at least loosen. You also might find it better to undo some of the wiring loom connectors to gain access to it.
Again from memory you should then see where the filter is located and it simply pulls out, it is more a case of clearing anything obstructing you from pulling it out.
When you are doing the job it looks more serious than it is as half the dash seems to be missing, but really it is a few screws and is fairly easy to see what needs to be un-done etc.
Just write down / diagram whatever works for you a quick plan of how you have taken it apart. Probably half hour to an hours job max