You have to take the hub off and remove the 8 bolts holding the rotor. If all your going to do is change the rotor, then you need to clean and repack the inner and outer wheel bearings along with the appropriate seals. If your front axle has not been rebuilt in the last 50,000 miles, I would recommend doing this at the same time. You will be almost halfway there in the disassembly process.
I would also replace the Pads with 100 (Land Cruiser) series pads.
If you plan on doing this your self. I also recommend going to the following link:
http://forum.ih8mud.com/index.php?
And selecting the 80's(LX450) tech link. This forum is great for helping with advice and how to's. There are links to how tos with photos, etc.
I also used the Factory Service Manual and its pretty straight forward. If you plan on doing any work your self, you need to get the manual.
In addition. A member of the forum (Cruiser Dan) is a parts rep for Toyota and gives everyone a 25% discount on parts.
The 80 series Land Cruiser and LX450 parts are almost identical with the exception of some trim and lights.
Good Luck
Ken