http://www.allpar.com/cars/chrysler/300M.htmlThe plugs are right under the coils, on top of the engine; use a flat-bladed screwdriver to push up the lever on the electrical connectors, and gently slide the connectors apart. Then carefully use a good quality Torx screwdriver of perfect size to take out the two screws - be very careful at first since they are attached very firmly and are easy to strip. Push down hard while breaking them free. Once the first quarter turn is done, they should unscrew easily, but they don't come all the way out. When both screws are unthreaded, gently pull out the coil, which is held in now by the airtight seal. Then the spark plug can be taken out with a standard 5/8 inch spark plug socket, replaced with new ones (with a dab of antiseize on the threads), and tightened to specifications using a torque wrench (aluminum heads!). The hardest part is getting those coil screws removed without damaging them.
