Drain bung is either at the bottom rear of the diff housing or to the N/S of it (2 types so check which yours is). There isn't a filler level plug, just a filler which is on the very top of the box about 4 to 6 inches in front of the gear selector near enough in line with it. It should be a hexagonal nut / bung with a loose fitting plastic or aluminium vent cap on it. Unscrew the whole bung, but don't remove or damage the vent as you may get leakage from it in the future.

Oh, and you'll probably need to remove the air filter housing and / or battery to gain access so make sure you have the radio code to hand to re programme it just in case.

You'll need to fully drain the box first then measure 2 ltrs of 75w80 semi synthetic gear oil and fill through the now removed bung. Use a small funnel, or if you are using the standard 1 ltr top up bottles of oil, the attached spout. Take your time doing either method as you'll probably get "blowback" and oil all over the place if you go too fast.