Reversing light change is a little awkward as there is a small nut to remove before the rear light cluster can be removed.
After you remove the small screw under the little flap next to the boot door on the interior trim and remove the centre pin and pull out the little fastener bung* next to the rear seat there is a small nut to remove when you gently pull away the trim. You will need an 8mm socket to release the little retaining nut that is in an awkward position and there is a danger of it falling inside.
You only need to release the tightness then you can use your fingers but I would suggest you use a cloth to fill in the void below and to the sides of the nut to prevent it falling into the panel if it slips from your fingers. The tip of the thread is smooth to help you avoid dropping the nut and this helps as a guide when replacing it.
You can then remove the light cluster from the outside but you may find it difficult to pull the little locking lugs from their very tight holding retainers.
There is one near the top and one near the lower area of the lens. They cannot be accessed and you need to pull the cluster away so they pop out of the retainers.
I found it easier to stand at the side of the car and push sharply on the side of the cluster towards to back whilst wearing a rubber glove. This should 'pop' the cluster off. Don't push too hard as you don't want to cause any damage; just a short sharp action should do it as you are only releasing the two little lugs from their retainers.
Just before you replace the cluster after swapping/changing your LED/bulb rub a little WD40 or vaseline on both the little lugs to make removal easier in the future.
*NB: You don't have to remove the little fastener bung near the rear seat but it does give you a little better access.