The rear diff and transfer case are very easy,..you can practically do these laying under the car without a lift. There's an obvious drain and fill plug for each. Both plugs are the same size and thread.
The front diff will require lifting the vehicle on jack stands,..removing the front wheels,..then remove the aluminum reinforcing plate under the engine ( 6 bolts). Then you'll be able to easily access the diff. Again, like the rear, the drain and fill plugs will be obvious. The rear diff takes a little more than a quart, the front a little less, and the transfer case takes 1/2 qt.(-- Fill to the level of the fill plug until it starts to run out--Mobil 1 gear oil for the diffs, ATF Dexron III for the trans case ).

Also, get an inexpensive hand pump for pumping the oil.
Torque---Diff plugs 50ft./lbs, Trans case plugs 35 ft./lbs