I did mine recently and it goes something like this.
Remove both of the outer rear lights by undoing the plastic headed retaining bolt from within the 2 side compartments. Then pull the lights out rearwards, there are 2 retaing lugs on the outer wing edge, but they will come with a tug.
Once the lights are out, on each side there is a plastic "pin" that pulls up and out at the back edge of the bumper and 3 screws from within the wheel arch (the bottom screw can stay in).
There are 2 screws that hold the valance from underneath.
Lastly there are 4x10mm nuts behind rubber grommets, 2 in the wheel well and 2 in the side compartments. Just be careful as you remove the nuts as they are incredibly easy to drop into the cavity!
The bumper will now carefully unclip from the rear wings and simply pull away.