Mike, download the Factory Service Manual from the home page of this site. The process is covered in there. Basically, bleed the air, support the engine block/oil pan with a jackstand, or it will fall, possibly injuring you, and definitely damaging the bike! Remove the fork caps, top of the forks, remove the springs. Remove the drain screws, at the outside base of the tubes -- wrap the tube with tin foil so as to channel the fluid away from the disk brake rotors, to avoid contaminating them! Catch the old fluid in a drain pan. Compress the forks, repeatedly (lift the front wheel up, as the jackstand is supporting the bike!), to evacuate all of the old fluid from the fork tubes. Put the drain screws back in place, fill with the correct amount of ATF/oil, compress the forks, repeatedly, to distribute the oil, and remove air pockets. Extend the forks, put the springs back in place, install the top caps, add the prescribed air pressure, and done.
If the fork oil is really old, you may want to add an ounce of
SeaFoam to each tube, before draining: pump the tubes repeatedly, to mix, and distribute the
SeaFoam, which will dissolve deposits of varnish, and other crud. Then you can wait 30 minutes, is you wish, to allow it time to work, or just drain it. Put in fresh ATF/oil, as above. If you haven't used
SeaFoam in the crankcase yet (follow directions on the can!), I recommend it: it will dissolve carbon, varnish, and other crud, within the engine/transmission. Ride it a short distance to warm it up to 180+ F (minimum operating temperature), after adding it, shifting through all gears, then change the oil and the filter, both. Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII