I removed the rear bumper already to replace with a new bumper. I have to remove the diffuser, sensors to the new bumper. I didn't do a DIY video this time but I have a video for the front bumper and its very similar.
You wont need any help its a fairly easy job. You need to take your time thou. As far as tools all you need is Jack, Jack stand for safety, ratchet, 10mm socket, Phillips screwdriver and Flat head.
If my memory serves me correctly. The bumper has 2(10mm) bolts that hold with the rest being plastic clips that you pull on to remove. You have to removed the taillight's. The nuts to are under the taillight to loosen the rear bumper. Then you remove all the plastic clips under the wheel that holt the bumper to the plastic lining.
You have the remove the tray on the trunk, there are some clips there that hold the plastic trunk lining that the rear bumper tucks under. After that remove the harness clip to the motion sensor and the bumper is free to come out.
I don't how familiar you are working with cars, but a shop would charge you about $250-$400 to replace the diffuser.
If I can find the instructions I will PM them to you.