2005 Lincoln Town Car Engine missfire loss of power

I have a Lincoln town car and it started to lose power. Then "service engine soon" light came on. I took it to the local autoparts to hook up the scanner. Scanner said cylinder #5 missfire. I replaced the spark plugs but engine still has missfire. The engine has been gradually losing power the more I drive it. Could it be coil #5 or could it be something else? Please Help. Thank You for your time. I've been out of work and I'm trying to do the repair myself I really don't have the money right now to take it to a shop. Thanks Again