Remove rear lamp clusters mounted to the body and put them in the boot - there are some screws revealed by opening the boot anyway.
Then only need to remove the screws that hold bumper shell to the black plastic mount that is revealed.. this black plastic mount stays on the car.
Number plate lights are a pain to disconnect once removed so a grovel around to remove the whole fitting plus connection maybe a good idea or else have a thin screwdriver around to
help removing the connection while supporting bumper on your knees.
Have a tressle (A frame thing for joinery; B&Q do plastic ones for under a £10) or similar to put the bumper on so that you avoid getting to the pain work.
Good wash makes it easier to get to the torx screws.. you may need new ones as they rust and become harder to engage with age .. I always managed but I guess you could slot them for a plain screwdriver with dremel or hacksaw if you fail to get engagement with torx bit.