Disassemble the planer by sliding off the bottom piece. Use the flat end of the bottom piece to turn the screw holding the blade in position.
Inspect the blade for any burs. A bur is a cut in the blade piece that causes the metal to stick up higher than the blade.
Clean the blade with a sponge and some water with a mild detergent. Remove any dirt and sawdust to avoid accidentally working it into the blade.
Dip the roughest whetstone in water, then rub the blade over the whetstone at a 30-degree angle. Continue until all the burs are removed from that side. Repeat this with the other side of the blade.
Rub the blade again with the medium then the smoothest whetstone to slowly polish out the scratches from the sharpening. Your blade is finished when the burs are completely removed and you can see your reflection in the blade.