Meg-Mo rotary mulching blades stay sharper longer than your usual mower blade, but they still may need the occasional sharpening.
To sharpen your rotary mulching blades, take them off your mower and put them in a vice. You should wear cut-proof gloves while handling these blades.
After you have it secured in the vice, begin using a metal file and stroke in one direction matching the angle of the blade.
Continue sharpening until there are no nicks left in the blade and it gives your grass a clean cut.