I changed my cabin air filter today. It wasn't bad. Took me 20 mins or so. I went with an OEM filter from the dealership since it was my first time changing this myself. I knelt on a boat cushion outside the passenger side door to access this.
I'm going to add on to Lenovo65's excellent instructions with some pictures.
I'm at 20k mi. and the cabin air filter was super grimy and had lot of particulate and pieces of leaves in it.
So, to take those clips off that hold that panel under the glove box. I'll show you in three steps. You can use a screw driver, but go ahead and get yourself a CHEAP plastic panel popper kit from Harbor Freight or Ebay. They're handy!
1) Position the tool as so.
2) Press towards the front of the vehicle to compress the clip.
3) Pry the clip downwards and it'll pop out. Then you can remove the panel.
The access door is white. The main hurdles for me where that white metal bracket, which I bent back a bit, and that electrical harness. I'm sure it pops off, but I didn't worry with that -- just worked around it. To remove the access door, pull the white tabs towards the rear of the vehicle to disengage the door, and slip it off (is a little more tricky than it looks, but you can do it).
The old filter came out pretty straightforward, although I had to yank it a bit to get it around those obstructions.
You've got to do some serious "FILTER YOGA" to get that new one in there. It's a combination of flexing, squeezing, and shimmying. I found most helpful to press the wires of that wiring harness towards the front of the vehicle to get a good angle.
Getting that door back on there is a little tricky, took a little doing, but got it. Buttoned backup, and works great!