what kind of short shifter, b & m comes with real good instructions. if not a b & m i think you can go to their website and they have a set, theyre pretty universal anyway. as far as i know you just pull of the knob and boot, then unscrew it, pull of the lower boot, and a few other things. this will explain it better:
http://www.bmracing.com/
go to products, manual transmission shifters, then nissan 240sx with sr20 (the ka is the same dont worry) the directions are in pdf form, last thing on the list of features.