it's real easy. take off the differential cover, and it's gonna drip everywhere...so have a big bucket or wide funnel or something.
crack 'em loose, let it drip, and loosen them more and more. but some axle fluid (not sure what exactly...but it's something simple). I used rubber silicone to seal it back up, or u can go out and buy a new gasket.
when u fill, the fluid level should be just at the bottom of the fluid check hole (the rubber bung in the diff cover)