There should be a fill plug on the right side of the rear casing. So you'll need an oil suction devise (looks like a large diameter bicycle pump) to suck out most of the old fluid. You can gravity fill the diff. with 1qt bottles and a long hose, but it's a bit of a pain - so get one of the cheap plastic oil fill pumps that can be placed in a quart or preferably a 1/2 gallon container to fill it. Only takes like 3.1/4 pints. If you have a limited slip then you'll also need 2-4 ozs of friction modifier as well as the 75W90 oil. The oil sucker & pump are relatively inexpensive at most auto parts stores. If you are thinking about using synthetic fluid, I recall that Ford now uses 85w140 in all their diffs.