HelloCustomer and welcome to JustAnswer.com!
Replacing the spark plugs
on your Crown Vic is actually pretty simple. Each spark plug has it's own ignition coil
bolted on top of it. You need to remove the single bolt holding the coil in place, then disconnect the electrical connector by squeezing the connector tab and pulling it off.
Next pull the coil straight off.. you may need to rotate the fuel injector
a little for clearance to get to the bolt (just spin it a little bit) and you may need to flex the coil a bit to clear the fuel rail tube.
Between the coil and the spark plug there is a short boot.. maybe 2 or 3 inches long. Once removed inspect the boot for signs of spark arcing (look for narrow gray lines) and if found you'll want to replace the boot.
Next using a spark plug socket and extension, unthread and remove the spark plug. It is recommend your blow out the hole with compressed air beforehand, but if you don't have an air compressor you'll probably be ok.. just shine a light down there and make sure there's no debris that can fall into the engine
Apply a small bit of anti-sieze to the threads of the new plug and install it. Then apply a small bit of di-electric grease to the end of the boot and reinstall the coil! Keep in mind these boots do not snap in place over the plug like traditional spark plug wires do, so as long as the coil sits flat over the hole, you're o.k.
Hope this helps! Good luck!