Changed the plugs...

I changed the plugs on my Jeep Cherokee Laredo 2001, 4 liter engine, 6 cylinder, but I still have the check engine light on. According to Advanced Auto, the computer logged that there was a missfire in the cylinder. I realize that it could still be the fuel injectors, but another question I have is there any chance that the computer would still keep the check engine light on after I left the battery terminal unhooked after a half hour? I heard that some vehicles need to have an automotive technician reset the computer inorder to clear the light.