Damn, that’s gonna be a huge project. I definitely suggest skinning and flensing the head first, because that will expedite the process since there won’t be as much meat to get off afterward. Flensing means you’re going to take a sharp knife or scalpel and cut away as much flesh as possible, removing the eyes, tongue, and anything else you can without damaging the bone.
After that you’ll have a few different ways to go- you could bury it, but depending on where you are it might be starting to get too cold for that to work quickly. You could also set it out in the open and let the bugs handle it, but you run the risk of bothering your neighbors if you have close ones or it being damaged by animals. The easiest way (outside of dermestid beetles) is to put it in a heated container with water and let the flesh rot away. It’s a smelly process and it takes a while, especially with such a large skull, but as long as you have a source of heat it should go relatively quickly.
I’ve seen some large heated buckets for livestock water containers at the local farm supply store, so that might be a good way to go. You could also use a large plastic tote with a fish tank heater.