Glow plugs in a diesel engine are the virtual equivalent of spark plugs in a gasoline engine. Although they function differently, spark plugs spark constantly when an engine is running, while glow plugs are only used to heat up the cylinder when starting, they are placed into the engine cylinder almost exactly the same way. Using basic tools that most do-it-yourself people will have, a glow plug gets replaced in virtually the same way as a spark plug.
Locate the ignition wires on your tractor. They will look just like spark plug wires, and can be traced to each cylinder on your tractor.
Start at one end of the engine or the other, and pull off the ignition wire from the top of the glow plug.
Push your socket onto the glow plug, attach your extension to the socket, attach your ratchet to the extension.
Set your ratchet to unscrew in a counter clockwise direction, and proceed to unscrew the glow plug.
Replace the plug with the same type that came out, screwing it in with a clockwise motion. Push the ignition wire back on. Repeat these steps for the rest of the glow plugs.