Use your owner's manual to locate your engine's spark plugs at the top of each cylinder. Look for any dirt buildup around the base of the wire. Clean the area around the plug with compressed air or a wet/dry vacuum. This helps prevent anything from falling into the cylinder once you get started. You may also want to use a clean rag and rubbing alcohol to clean away some of the dirt.
Before you dive in, remember it's easiest to change your spark plugs one plug at a time. Accidentally plugging the wrong wire boot into the wrong spark plug can cause problems. It's easiest to avoid confusion if you remove and replace each plug individually. Once you're finished with the first plug, you can move on to the next one.
You should see a wire connected to the spark plug. Remove the wire by pulling on the boot -- the connector at the end of the wire. Spark plug wire boots are usually rubber or plastic. Do not pull on the wire itself or you may damage the connection between the wire and the spark plug.
If your spark plug wires have a rubber boot, grip the boot and twist it gently to the right and left. This should help loosen the connection. If a boot is particularly stubborn, you may need to use a pair of boot pliers to grip it and unplug the wire. Wires with a plastic boot tend to be easier to remove -- just grip the plastic and pull gently.
Once the wire is removed, you can use your socket wrench with the spark plug socket to remove the seated spark plug. Fit the socket around the spark plug and turn the wrench counter clockwise. If the cylinder is at an odd angle, use a universal joint to reach it. The spark plug should unscrew easily. If you encounter resistance, stop. Forcing the spark plug to turn could break the plug or damage the engine. It's better to visit a mechanic to remove a stubborn spark plug than to perform expensive cylinder head repairs.
In most cases, the spark plug should unscrew easily. Once you've removed the old spark plug, set it aside. Inspect the threads. If they appear dirty, use a clean rag and some rubbing alcohol to clean them. Now you're ready to insert the new spark plug.