How to change spark plug and tools to used
You will need a 5/8" spark plug socket, a 3/8" ratchet, a 2" X 3/8" extension, a 6"X 3/8" extension, a 3/8" universal joint, and a lot of patience. The spark plugs on an Express are very hard to get to.
First, remove the glove box bezel (the trim around the glove box) by gently prying it off. You may need a small flat-tip screwdriver to do this.
Second, remove the glove box (located underneath the drink holders in the center console beneath the radio), it just snaps in at top.
Third, remove the engine cover. There are four bolts behind the glove box, remove them. Remove the left and right side lower dash panels (they snap in). Release the four clamps, and wiggle and rock the engine cover away from the dash.
Now you get to try to remove the spark plug wires, which will be stuck quite firmly due to the many hours of engine heat. Once you have a wire off, you then have to finagle the spark plug socket onto the plug. You will have to try various combinations of universal/extension/ratchet to accomplish this, and the plugs will be stuck quite firmly as well. Do this one wire/plug at a time.
Gap your replacement plugs to the spec in the owner's manual, usually .060".
Installation is the reverse of removal.
Good luck, and if this helped, please remember to vote/comment.