The blades are just held on by a nut and bolt. I would start off with an impact wrench. However that never seems to work as the bolt will spin. The next step would be to tack weld the bolt to the blade and then use an impact wrench to loosen the nut. If you do not have an impact wrench a long 4' bar on a wrench would work. Another option would be to cut the bolt but there is no room to work any tools under these.