Black and Decker electric hedge trimmer blades are made from hardened steel that will not typically lose their sharp edge or require resharpening. If the blade comes into contact with a hard object such as a stone, wire fence, or glass, the blade could be nicked. Some nicks will need to be removed by sharpening the blade.
Unplug the trimmer from the power outlet. Set the trimmer on a flat surface.
Place the file or sharpening stone on the base of one of the blades that needs to be sharpened. Run the file along the edge of the blade all the way to the tip. Repeat several times.
Sharpen any other blades on the hedge trimmer that need it by following the same steps. It is not necessary to sharpen all of the blades.
Always wear proper eye protection when sharpening an electric trimmer to prevent fragments from causing eye damage.