You will need a socket for the spark plugs, one that will hold a plug to pull it out. You will need an extension to reach down in to the well that the plugs rest in and of course a rachet. Gently take one wire off and remove the plug. The new plug should be checked for gap and then carefully put in the engine to ensure that it does not get hit on the bottom that could cause the gap to close. Tighten it carefully to specs and replace the wire. Go on to the next ones. Keep them in line as you take them out so you know which came from which cylinder. I say this because the plugs are fanstastic indicators of the way the car is running.
I look at the plugs to see what is deposited on them, are they burnt, was the gap close to the original gap, etc. Another thing is to see if they look the same. Then you can determine whether the engine is consistant. If they look the same the cylinders will generally look the same inside, the compression will probably be close. A difference could indicate a weaker set of rings or an injector that is not performing correctly. You can find color pictures on the internet to indicate the problems indicated by plugs. Good luck!