Pelican Technical Article: Installing a Boxster Short Shift Kit (SSK) and Replacing Boxster Shift Bushings - 986 / 987
There are a number of other sites to find the install instructions as well. The instructions, especially the pictures, have much to be desired but it's not much of a job.
Again, as per earlier advice, I'd also recommend turning the shifter lever around so it leans the other way (away from driver versus towards), you'll be much happier. Why it comes the other way I have no idea.
I used the stock shifter knob and leather boot... looks perfectly stock but everything functions much better.