its fairly simple, crawl under the rear of your 4runner and near the bumper should be approx. 6-8 clips. you just squeeze with a needle nose pliers and push/pop up (toward the sky). Be sure to get all the clips before you stand back up and try to lift the plastic piece off. I always forget some clips in the corner and end up crawling back several times.
Since I got my 4runner painted (just picked it up today), I guess I should touch this part up since it looks awkward.
cheers