Whether one of your bulbs has failed, or you simply want to change them in order to improve the light output of your reversing lights, it's an extremely easy job. No special tools are required; all that's needed is something to pry off the fasteners that secure the lining to the boot/trunk lid.
A prying tool like this one is ideal. The fasteners are ribbed and require a decent amount of effort to pop loose, but a "claw"-style tool makes light work of them. I suppose they could also be removed with something else (screwdrivers, pliers etc), but they run the risk of being damaged in the process.
No need to remove the lining fully, just enough to gain access to the bulb holder.
A small twist of the holder will release it from the light casing and allow access to the bulb. They're a "wedge" fitment and simply pull out.
The replacement bulbs, ready to be fitted. The fitment type/size is W16W. Many different brands of varying quality and cost are out there, but I chose to spend a little extra ( £20) on a pair of premium quality bulbs that promise to be long-life and brighter than average.
One of the new bulbs in place. Always a good idea to check that it works before putting everything back together. If it doesn't initially light up, just pull the bulb out, rotate it 180 degrees and re-fit.
One side done. Just repeat the same process for the other side.
Job done. Even on a bright sunny day, they're clearly visible and appear to be quite a bit brighter than the OEM bulbs I took out. They should be amazing at night!
So there you have it. This task is extremely easy, takes all of 10 mins and probably doesn't even deserve to have a tutorial for it. Personally-speaking though, I always find it handy to have some kind of reference to check out before I attempt to pull my car apart, so hopefully someone finds it useful.