It's very, very straightforward. You'll need at least 5ltrs of Dexron IID or III; a large container to collect about 4.5ltrs of waste oil; a tool to get the oil into the 'box (I use a 500ml syringe).
Empty out the old oil after warming up the vehicle by undoing the small allen screw sump plug - leave to drain for at least 30mins, the longer the better.
Then locate and remove the level/fill plug (1/2" plug) and put in as much oil as you can get - approx 2.5ltrs - then start the engine; put the transfer box in neutral and cycle through all auto positions (pausing 2-3secs in each one) and back to P.
Now put more all into the 'box, perhaps 2ltrs or until the autobox dipstick shows full. Then refit the fill plug and enjoy the warm glow of being able to DIY !!!
Dave