If you notice that your grass looks brown and ragged after you cut it, you probably have dull blades on your lawn mower. A dull blade rips the grass (instead of cutting it cleanly) and cause your whole yard to look rough and ragged. If you don't want the hassle of transporting your mower to a shop, so they can remove and sharpen the blade, do it yourself. You'll need a grinder in order to get that sharp edge.
Park the machine on flat level ground and set the parking brake.
Turn the machine off and disconnect the power by removing the negative cable from the battery. Use caution not to touch the positive battery cable to anything that is grounded, as it can cause the cable to spark and ignite the battery or fumes from the fuel tank.
Remove the deck if necessary in order to access the blades.
Block the blade from turning by locking it in place with a pair of channel lock vise grips or by putting a piece of wood in between the blades so that they cannot turn.
Use a ratchet and a breaker bar to loosen the nuts holding the blades in place.
Use a grinder to flatten the cutting surface on the front of each blade, so that nicks or dings in the blade are gone. You want the surface on each side to be flat, without indentations or scratches or pock marks. Wear safety glasses and work gloves while using the grinder.
Start at the tip of the cutting surface on the front of a blade and grind back at a 45 degree angle until you meet with flat surface of the blade. Repeat with each blade along the length of the cutting surface.
Turn each blade over and grind a steep, almost flush angle along the back of the cutting surface to meet the 45 degree angle on the front of the cutting surface. This will create a razor-sharp edge.