Just wanted to add a couple of points to jeffsr's advice. If you have access to an air compressor, you could blow some air around the base of the spark plug after you pull the plug wire off. This will get rid of the lose dirt around the base that may drop into your cylinder once you remove the old plug. Also, please use put a small amount of anti-seize lubricant on the threads of the new spark plug before you install it. This will prevent the plug from seizing in the cylinder head and will greatly ease the next plug change. Good luck.