They are pretty easy to get to, jack up the back of the car and remove the rear wheels, and the fender liner that is toward the front of the car.
Change Spark Plugs & Tubes
Pelican Technical Article: Replacing Boxster Spark Plugs and Coils - 986 / 987
I use this tool when doing spark plugs and it has been working great.
GearWrench 80546 5/8-Inch x 6-Inch Swivel Spark Plug Socket - Socket Set With Spark Plug Socket - Amazon.com
Steve