Change the spark plug for 1999 pontiac montana

Ok, based on the firing order from your vehicle there are (6) cylinders, and (3) are on the front of the engine and (3) are on the back. I have never even looked under the hood of one of these types of vehicles, however, You MAY need to remove the large plastic engine covering (not sure for your vehicle). If that is the case you may have to remove the engine oil (tube). The cap that you open up to add oil, twist and pull on the actual tube and it should twist off (if needed on this vehicle). Once this is removed if requiered on your vehicle, you can then remove the large plastic covering to have access to each cylinder. Once the large plastic covering is removed, put the oil fill tube back in place for the moment so no contamination gets in your engine. I would start with the back side first because that is hardest. I checked on Autozone.com and they have it listed for this vehicle that the iginition coil is set up on the left side. You should see six wires coming from this area with (3) going to the front and (3) going to the back of the engine. Start on the back side with the whichever of these wires/cables goes to the left side of the back of the engine. Please only do one at a time to avoid confusion as to the placement. What I would do in all honesty if you are doing the tune-up is to replace the spark plug wires as well. What I have used on all of my vehicles and have had great success is NGK plugs and NAPA auto parts has plug wires Belden Maxx (this is only a suggestion and I am only sharing what has worked well for ME). OK, prior to starting what you will want to do is take each individual plug one at a time, and using a spark plug gap tool (readily available at all parts places) Place the non-porcelin end (the one that has the arc in it) into the gap tool at the lowest end and slide it around until you have reached the required gap. For this vehicle it is .60 Even if they tell you at the factory it is pre-gapped and you don't have to check it, believe me it is always a good idea. I just did a vehicle and all (6) were not gapped correctly. Put each one back in the box until needed. Once you have done this,starting on the back of the engine left side find the spark plug cable/wire that goes to that side and where it goes into the engine it will have an end with a boot on it. This covers the spark plug. Twist this boot off the spark plug, it may take some effort. Once that is off if you are replacing the spark plug wires take this one and match it up with the new set (They will be different lengths). Now for the fun part, removing the plug. Using a spark plug socket (available at parts places, has rubber on the inside to grip, and protect the socket) a small extention and your ratchet, place this over the plug and apply pressure until the plug begins to turn. Once you have the old plug out, place the new plug in the spark socket and thread it in by hand (it will be in the socket but don't use the ratchet yet. Once you have the plug in as far as you can by hand tighten it down with the ratchet (don't overtighten). Place the new or old spark plug wire (boot) over the new plug and move on to the next cylinder. Do each one the same way (ONE AT A TIME, to avoid confusion). This is a long explanation but I hope it will help someone...Thanks