Differential Oil Change

Jack rear of car up and support with jack stands. Reversing on ramps also works great.

IMPORTANT! Ensure you can remove the filler hole before attempting to remove this nut.

Clean dirt and undercoating from upper filler plug with a wire brush then remove.
Use a penetrating oil or heat if necessary. 

Lower drain plug. It can be turned with a 1/2" ratchet.
Clean debris and under coating with a wire brush and spray with penetrating oil if needed.

Remove the lower drain plug and drain into a catch pan.

Inspect lower drain plug for trapped metal filings. It is magnetic and will capture thsm. 
The amount in the photo is not great but acceptable.

Flush the differential and refill until it over flows out of the top hole. Use a hand pump or the "IV" method.
Use a 75W90 synthetic oil such as Redline .