i installed my tenzo short shifter myself....not too hard, just don't put it on backwards...I'll try and remember...
1) take out your center console
2) remove the shift knob and boot, should be able to do that from inside
3) Jack your car up, the higher the easier, and you have to disconnect this screw thing from underneath, i'm pretty sure it's the part that connects the shifter to the linkage thing (the long black pole that goes from the shifter to the front of transmission. It looks like you wont be able to pull it out because of the ball thing on the shifter, but you have to bring it down from underneath.
4) once the old one is out just put the new one in and hook everything back up and make sure it works.
I am terrible at directions, plus I installed mine like 2 years ago, so I don't remember much. I put mine on backwards at first so dont do that. And If you got a generic one, some generic ones arent actually a short THROW shifter, their just a shorter stick. That won't help with shorter shifts. So if you get it installed and it doesnt shorten the length of your shifts its pretty much useless.
I hope this helps at least a little.