Here's how to replace the bulb in the boot.
1. Take the bulb holder / light cluster / light box (whatever you want to call it) out of the plastic trim / wall of the boot. To do this you need to insert a small flathead screwdriver or anything else that's narrow and flat in the little hole that I've marked red, then push away from the wall.
2. Once you've removed the light cluster, disconnect the cable from it. You need to press on top of the white plug to release it and whilst pressing, pull the plug out.
3. You need to release two tiny plastic bits (one on each side) of the enclosure that's on the back of the light cluster. Simply press the little plastic in and at the same time slowly pull the enclosure upwards so it doesn't lock again. Do the same on the other side. If you've done it correctly it'll start to lift off the light.
4. Gently lift and pull the enclosure off the light cluster. It'll come off fully and you'll have access to the bulb.
5. You can replace the bulb with a different W5W type bulb. Either standard halogen or LED one. Simply pull the bulb out and insert a new one
*. If you can't remove it, use a screwdriver to push the bulb out from behind.
* It's worth noting that if you insert an LED bulb and it doesn't work, try to take it out and re-insert it the other way (turn it 180° so the positive and negative are on opposite sides). It should work. If it still doesn't, try another bulb.
Personally I've used an LED one as I prefer the look of the white light and they are usually (always?) stronger than the halogen one. Got mine from Amazon. Set of 10 for £6. Currently same set is £7.50 (as of 15th Feb).
6. Once you've changed the bulb, put the enclosure back on. (Or don't. Whatever you prefer. Some cars don't have them so it won't hurt anyone if you chuck it in some corner of your garage.) Simply align it with the light, like it was before taking it off and press down so it locks into place.
7. Connect the cable (only one correct way to insert it so can't go wrong here).
8. Push the cable behind the boot wall. Insert the light cluster into the hole (plug first - so the side closest to the seats) and gently push the light in until it clicks.
Hope this little guide helps with the boot light! I'm planning to make a long post regarding stuff I've done to my Grandland, along with guide a on how to do those little tweaks or modifications, once I've finished everything.