Here are the instructions on how to replace them:
http://www.pedrosgarage.com/Site_3/Change_Spark_Plugs_%26_Tubes.html
But, if you're getting a misfire code, first check to see that cylinder 5 is connected properly.
Sometimes the coil's connector get loosened and you'll get a CEL.
My car is at 195,000 miles and I still have all of the original coils.
Happy Boxstering,
Pedro