How to change the blade on Jonh deere gas edger. The blade keep moving when I try to remove the nut ,also in which direction I should turn the nut ?

Put the blade against the ground.and try .
Should come off to the left.
Luck

DG is correct. You can also clamp the blades with a metal "C" clamp and turn lefty loosey, counterclockwide. There are afew blades on machine that attach with reverse thread so check to see the blade rotation direction, loosening will be the opposite of rotation.