Probably a thread similar to this has been posted before, but having just tackled the issue, I thought I would post the simple procedure for other Newbies like me:
Tools needed: #25 Torx wrench, Flathead screwdriver
Procedure:
1. Open bonnet(hood) - air filter box is located at the rear of the engine.
2. Unclip mass airflow sensor just forward of the air filter box on the outlet tube.
3. Loosen the clamp on the outlet tube to allow box lid to be removed.
4. Unscrew the 4 Torx screws attaching the lid to the filter box body.
5. Lid is attached on the back by 3 guides - just pull forward to expose the air filter element.
6. Put in the new filter and reverse the procedure to reassemble.

I just replaced the stock filter with the high-flow filter from Alta - works great!