how do I change the spark plugs at the firewall side for a chrysler t&c 2002 3.8 V6?

No tricks involved, just the right extension on the plug socket. Hint, go in from the drivers side behind the manifold.

You may not need to replace them . My 95 new Yorkers has had the plugs replaced 8 years ago. Old ones were clean. Car has 70000 mi . Check the ones that you can get to. If they are clean no need to change them. My 95 gets 20 mpg in the city.