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The only thing that you may need to remove to give yourself more room is the air intake tube. You may need a large extention and a spark plug socket to get the plugs out. Other than that it's straigh foward.
Grasp the plug wire and carefully twist the wire to release the retainer from the spark plug. If the plug wire is stubborn, a pair of special removal pliers is recommended to remove the wires from the plugs
Carefully remove the plug wire from the cylinder head
A special spark plug socket with a rubber insert is needed to remove the spark plugs. Typically the spark plugs require a 5/8 socket
Using a suitable drive tool and the special socket, loosen the spark plug and . . .
. . . remove the spark plug from the engine
Clean out the spark plug bore and threads before installing the new spark plug
An inspection of the old spark plugs will give a general idea of the condition of the motor, compare the spark plugs to the chart in this section
A piece of fuel line or a small hose is useful in installing the spark plugs to avoid stripping the threads