The first thing is to remove the rear recovery/tow hook. You will not put this back onto the car. If you wish to keep the recovery hook, you will have to drill a slot for it in the diffuser. I will be removing mine.
Three bolts hold it on. Two that mount straight up to the frame, and one more on the side. Although both ends are in a bolt shape pattern, only ONE is actually removable! The other is welded on. Don't do what I did and accidentally snap it off (on a previous mod). If you do, don't worry, it's not going back on the car. And if you're putting it back on you just need to replace it with a nut.
You will need a 17mm socket to remove the bolts.
Once loosened, the brackets should slide off. You will not be using these anymore.
In the bag of hardware they've included, the larger pair of bolts, washers and nuts are the replacement. I ran into a problem when installing mine. I had to go to Lowes to buy a larger washer since the ones they've included are barely larger then the diameter of the bracket. I contacted APR about it, but they failed to get back to me.
Shown is what they included for this part, and the larger washer I had to buy.
This is what it looks like after installing it properly.