You woosy 4-pot boys have it easy.
1) First unbolt the 4 screws holding on the lid of the airbox. You'll be able to lift the lid but not take the air filter out, as the lid is half way inside the front wing.
2) Undo the single nut on the bracket next to the battery. From memory (car's too far away for me to go look) this just holds the air sensor in place.
3) Undo the funny circlip that holds the rubber tube coming out of the air sensor to the injection box.
4) There's a connector block attached to the air sensor. Now it's loose, you should be able to unplug it (it has a clip holding it in place, so remove that first).
The rubber tube, air sensor and airbox lid should now be completely unattached to anything else and can be removed from the car, with a bit of jiggling about.
The refit is the opposite way round but be warned - that circlip is very awkward to do up again. May be worth replacing it with a big jubilee clip (or have one ready) in case it gets on your nerves or you can't do it) - you need a good pair of pliers.