First you have to remove your bumper...There are 2 10mm bolts under the car as well as 2 phillips screws under each wheel well...Undo all of these and the bumper slides off...You will be working with the bumper mostly so set it on a cloth and get comfy...

The upper opening comes off by undoing some screws I believe...It has been a while so look around and you should see how it comes off...There are screws that hold the outer painted piece to the inner black piece...Undo the screws and pull them apart...Cut out the center of the black piece and toss the scraps...

You should have a 6" x 3' piece of gutter guard handy...You can get it at home depot or lowes...I cut the gutter guard in the shape off the black piece, leaving a little overhang. Put the gutter guard over the black piece and press down on it with the painted piece, wedging the piece together. Put the screws back in to hold the two pieces together along with the piece of grill between them...Apply pressure while screwing the screws back in so you don't strip any of them cause they will be a tight fit with the grill in place.

After that step just assemble the whole bumper and put it back in place. The lower grill can simply be cut out...It doesn't pop out or anything...Make sure you sand the sides from where you cut on the bottom so no jagged edges show if you do this. You will probably need a different grill piece for the bottom cause the gutter guard that comes in larger sizes is too flimsy...A friend of mine is getting some strong mesh for my bottom opening and using apoxy to hold it on...Other people have used zip ties (WTF??) but I don't like this idea...I will tell ya how it turns out when she finished.