Hello & Welcome,
Here is the procedure, including a few pictures.
Removal & Installation
NOTE All models were originally equipped with platinum-tip spark plugs which can be used for as-long-as 100,000 miles (161,000 km). This holds true unless internal engine wear or damage and/or improperly operating emissions controls cause plug fouling. If you suspect this, you may wish to remove and inspect the platinum plugs before the recommended mileage. Most platinum plugs should not be cleaned or re-gapped. If you find their condition unsuitable, they should be replaced.
When removing the spark plugs, work on 1 at a time. Don't start by removing the plug wires all at once because unless you number them, they're going to get mixed up. On some models though, it will be more convenient for you to remove all of the wires before you start to work on the plugs. If this is necessary, take a minute before you begin and number the wires with tape before you take them off. The time you spend here will pay off later.
Disconnect the negative battery cable, and if the vehicle has been run recently, allow the engine to thoroughly cool. Attempting to remove plugs from a hot cylinder head could cause the plugs to seize and damage the threads in the cylinder head.
Check for access to the plugs on your vehicle. The wheel wells of most vans are designed to allow access to the sides of the engine. A rubber cover may be draped over the opening, and it may require removal of 1 or more plastic body snap-fasteners (which are carefully pried loose using a special C-shaped tool) before you can move it aside for clearance. If this is your best access point, raise and support the vehicle safely then remove the front tire and wheel assemblies. NOTE On some models, the engine cover may be removed to provide additional access to the spark plugs. This will be necessary if you also plan to check the spark plug wires at this time anyway.
Access to the spark plugs is through the wheel-well on most Astro and Safari vans
Carefully twist the spark plug wire boot to loosen it, then pull upward and remove the boot from the plug. Be sure to pull on the boot and not on the wire, otherwise the connector located inside the boot may become separated. NOTE A spark plug wire removal tool is recommended as it will make removal easier and help prevent damage to the boot and wire assembly.
Disconnect the spark plug wire by pulling on the BOOT, NOT THE WIRE
A spark plug wire removal tool is recommended to prevent wire damage (and to make it easier)
Using compressed air (and SAFETY GLASSES), blow any water or debris from the spark plug well to assure that no harmful contaminants are allowed to enter the combustion chamber when the spark plug is removed. If compressed air is not available, use a rag or a brush to clean the area. NOTE Remove the spark plugs when the engine is cold, if possible, to prevent damage to the threads. If plug removal is difficult, apply a few drops of penetrating oil or silicone spray to the area around the base of the plug, and allow it a few minutes to work.
Using a spark plug socket (usually a 5/8 in. socket on these engines) that is equipped with a rubber insert to properly hold the plug, turn the spark plug counterclockwise to loosen and remove the spark plug from the bore. WARNING AVOID the use of a flexible extension on the socket. Use of a flexible extension may allow a shear force to be applied to the plug. A shear force could break the plug off in the cylinder head, leading to costly and frustrating repairs.
Loosen the spark plug using a ratchet and extension . . .
. . . then carefully unthread and remove the plug from the cylinder head
Inspect the spark plug boot for tears or damage. If a damaged boot is found, the spark plug wire must be replaced. As mentioned earlier, this is an excellent time to check each of the spark plug wires for proper resistance and/or for damage.
Using a wire feeler gauge, check and adjust the spark plug gap. When using a gauge, the proper size should pass between the electrodes with a slight drag. The next larger size should not be able to pass while the next smaller size should pass freely.
Carefully thread the plug into the bore by hand. If resistance is felt before the plug is almost completely threaded, back the plug out and begin threading again. In small, hard to reach areas, an old spark plug wire and boot could be used as a threading tool. The boot will hold the plug while you twist the end of the wire and the wire is supple enough to twist before it would allow the plug to crossthread. WARNING Do not use the spark plug socket to thread the plugs. Always carefully thread the plug by hand or using an old plug wire to prevent the possibility of crossthreading and damaging the cylinder head bore.
Carefully tighten the spark plug to 124 inch lbs. (14 Nm).
Apply a small amount of silicone dielectric compound to the end of the spark plug lead or inside the spark plug boot to prevent sticking, then install the boot to the spark plug and push until it clicks into place. The click may be felt or heard, then gently pull back on the boot to assure proper contact.
I hope this helps.
Take Care, Greg A.