First off to do this, You will need the correct grade gear oil and a 3/8" square drive bit, I just use a 3/8" sliding T bar or ratchet and a Drain pan, You will need about 2L of oil. Buy a 5L bottle, you will be saving money especially if you replace it reguarly or are doing the front diff at the same time.
Chock the front wheels and jack the car up on some stands.
The top hole is to fill it, The bottom hole is to drain.
Place your drain pan under the diff. Remove the top plug first, It would be a pain if you drain the oil first then realising you can't undo the plug to fill it back up.
Once all the oil is drained, put the drain plug back in and tighten.
If you bought a 1L bottle, they usually have a spout that pulls out to help pouring. Alternatively you can use a funnel with a length of hose. Pour the oil into the filler hole until it starts to come through the hole. Then replace the plug and tighten.
I use an oil syringe/pump. It makes filling the gearbox and transfer case much easier. Put the hose into the bottle and pull on the lever to fill, push the lever to release.
Make sure you dispose of your oil thoughtfully, You can dump your oil at most mechanic workshops or at your local council tip in the designated area. Don't put it into the used bottle and place it in the bin which will end up as landfill, the bottle may brake and spill oil into the ground!! That will make baby jesus cry and Chuck Norris will hunt you down for revenge.
