I have a Craftsman Edger/Trencher model 247.762660. I need to change the blade (or sharpen it - your thoughts as to which one is best?). I bought a Craftsman 15:16 wrench for one nut and a 15/16 socket for the other which are the correct size, but and they won't budge (either way). What is the correct direction to unscrew the nut, and what else can I do to take it off?