If the blades on your machine are plastic, then the chances are you’ll be supplied with several replacement blades at the point of purchase. If they’re metallic, however, there are two ways you can go about restoring your blade’s edge if need be:
By hand
Place the blade in a clamp and use a file or grindstone to hone the edge, keeping the blade as close as possible to a 45-degree angle, as seen in the following video:
With a bench grinder
Get your protective goggles on and sharpen the blade by applying pressure to the angle of the cutting edge against the grinder.