I'm afraid you need to access the air box from below. Jack the car up safely and remove the bolts holding the skid plate in place, these are torx if memory serves. Once removed you will see the air box and the two clips which hold it shut. Unclip them and the smaller section of the box can then be opened and you'll see your prize. P.s. Don't do what I did and lie directly under the box, pull the filter out and drop 12 months worth of dust, leaves and crap in my eyes.
It is a pain in the backside I'm afraid but not too difficult. Just make sure you have some torx bits to hand. Good luck!! :thumbs::thumbs: