Save yourself some cash, by doing this yourself, says Cenek Picka, of the Advanced Technology Institute.

Check your owner’s manual to see which plugs you need and when to change them. Replace them one at a time to ensure proper firing order

Blast away the crud

With your engine completely cool, use compressed air to blow away dirt or debris around each spark plug. This reduces the risk of particles falling into the combustion chamber and causing major engine damage.

Clear your path

If your car has an older engine, 
the spark plug wires may be covered by 
rubber boots. The best way to remove the boots is with your fingers by twisting and pulling up on it. Never pull on the wires themselves.
If your car has a newer engine, 
coils are attached to the plugs. Pull back 
on the tab of each coil’s harness, and then 
grab the coil and slowly pull up. You’ll hear 
a pop of the vacuum seal breaking and the coil should slide out. Don’t use tools – they may snap the coil.

Remove the plugs

Use a ratchet wrench, spark-plug socket, and extension to unscrew the plug. If the plug won’t budge, it could be jammed. Put everything back together and take your car to the shop. You could damage the plug threads if you force it.

Set the spark plug’s gap

The space, or gap, between the two electrodes must be set for your engine. Use a gapping gauge to adjust the gap according to the figure in your owners’ manual. The gap is correct when you pass the gauge between 
the electrodes and feel slight resistance.

Make the swop

Apply a small amount of anti-seize lubricant, like Q10 to the threads of the spark plug to prevent corrosion, and use the socket and extension to carefully insert the plug. Be careful not to bump the electrode. To avoid cross-threading, give the plug a twist in the opposite direction so the threads align and then hand tighten. Finish tightening with a torque wrench per your owner’s manual. Reconnect the boots or coils.