Good advice so far. Do it when dormant, dig a huge root ball, and be sure to prune it back.
I'll add 3 things....moved many trees like this. Not sure where you live, but I would do it when you can still water it. I transplant trees like that here in the Northeast in mid to late fall and water the heck out of them for many days. The water is not so much for the tree as it is to help compact and compress the soil to remove root killing air pockets. I would also be sure to stake the tree for several years. Lastly, I always go in in the later summer or early fall with a sharp spade and dig out the perimeter of the root ball without actually moving the tree (there's probably a term for this nurserymen use). Basically I am severing all of the roots in what will eventually become the rootball. This encourages an explosion of new growth within that rootball and when you do move the tree months later all of those new roots will help provide balance between the roots and crown. I'd still prune it back a little though.
Good luck.