Find a flat surface to work on and make sure you unplug the electric hedge trimmer and place them on the table top with the blades facing away from you. Using a pair of pliers or a vice grip, grasp the screw or bolt holding the blades in place. Turn the bolt or screw and remove it in order to remove the two blades. Place the blade in a vice and grip it so it cannot slip. Start with a metal filer and slide it down the length of the blade. Start from the inside or bottom section of the blade part and keep it going till you get to the tip. Sharpen at an about 40 degree angle several times but do not do it to the flat edge of the blades. Repeat all of this with the other blade.
After this test the sharpness by holding a piece of paper above the blade and seeing how much force it takes to cut. If it doesn't cut easily you will need to repeat the sharpening process. Now you need apply a thin coating of oil to keep them from rusting. A good oil for this is linseed and do this before bolting them back together. Now just replace the screw or bolt back into place using pliers or a vice grip and tighten so each blade is securely in place.