The oem fluid is synthetic and very good. It doesn't hurt to change it if you've got some miles.
Assuming that you have the stock stamped cover, you'll need to remove it to drain. The the fill hole is on the front side of the housing. 2 quarts plus 1 bottle of oem friction modifier. You'll also need a new gasket or rtv. If it were me, I'd get the steeda finned cover with drain and fill plugs plus a lube locker gasket from lmr.
Finned cover or the FRPP aluminum cover will be a nice upgrade over stock. I've been running the RP oil with 4 oz Ford fric modifier. No problems, but not sure if any real difference over the Ford fluid.
With the FRPP cover, I needed about 2.5 qts to fill the pumpkin.