Ford Focus from 2002-2007 (as far as i know)
Your Ford Focus air filter is located on the passenger side.
you must make your windshield wiper blades point upwards.
Pop the hood of your car and lift.
Right beneath where the windshield wiper blades normally rest you will see the black dimpled plastic liner (don't know how else to explain it)
You will see 4 clips beneath it clipping it in.
Pop all four clips
Before you try taking it off, look at the black dimpled protector and see if there is a little black round cap that is right in the middle of it. If there is take the cap off and take out the screw (flat head)
once removed and clips released take off the black dimpled protector and walla there is your air filter.
What you do from there is up to you.
hope that helped