My video below shows how to change the spark plugs on a 1994-2004 Fourth Generation Ford Mustang with the 3.8L V6. Changing the spark plugs on this generation mustang is somewhat difficult, most of the plugs are simple, but a couple will give you some problems.
And while you are in there working on the plugs, it might be wise to replace the ignition coils. Surprisingly, the whole set is only around $45 (May 2016) http://amzn.to/1Z464Ve