We blow compressed air from a compressor or pump into the spark plug socket to remove any dirt.
We change the spark plugs one by one so as not to mix up the order of connecting the wires.
We remove the spark plug tip.
Using the spark plug wrench from the set or a special 21 mm head, unscrew the spark plug.
Before installing a new spark plug, check the gap between its electrodes (see Adjusting the spark plug gap) and make sure that the sealing washer is in place and not deformed. First, screw the spark plug in "by hand", then tighten it with a wrench (see Applications).