At the back
To remove the bumper you'll need to remove the 2 screws on either side that are situated in the boot foor wells, they are the ones with the very large spacers if they haven't been switched from the originals.
Then you need to remove the other nuts at the back, can't remember if you can do that from under the bumper itself or from under the car at the back...
With the body kit part, I'm not sure if tech 1s have clips holding it in place but just visually work your way round to check.
I'm sure it's just held in place by the bumper though, someone can correct me if I'm very wrong