There are several videos on youTube that show how.
Ensure the machine is disabled and can not suddenly start up. Remove spark plug wire.
Tip the machine on its side so that oil and fuel will not spill out
Jamb the blade with a wooden block to stop the it from moving.
I clamp the block with G Clamp against the skirt.
Use a well fitting spanner (wrench) on the centre bolt.
Strike the spanner sharply with a mallet - anticlockwise to undo.
Wear gloves.
https://www.youtube.com/watch?v=Wv9dcBlbWhw
Good Luck..., April 2016
