Frank,
Marty is right. The only factory installed water filter on the 2002 Patriot is for the icemaker. The water pressure concern that you described is either caused by a restricted screen at the water inlet/supply hose, or the factory installed pressure regulator that is built into the city water inlet.
If you have a water filter, other than the icemaker filter, it was owner installed. Owner installed filters are virtually always in plain sight, where they are easily serviced, because the installer knows that he will have to service it. Unlike the people who build these things, and let someone else worry about the service issue.
Gerald