A can opener can cost around $5 to $20 or more, depending on the brand and quality of the item. When the can opener's blade goes dull it can be annoying. Frequently people put off replacing the small appliance, struggling with difficult can opener instead. Perhaps the can opener doesn't need to be replaced, but the blade simply needs sharpening.
Clean the can opener. Often food particles from cans build up on the opener's blades can cause it to stick and resist opening a can easily. Soak the blade in a little bit of soap and warm water for an hour, then use an old toothbrush to thoroughly scrub the blade. Test the can opener to see if it works better.
If the can opener blade still seems dull, tear off a long strip of aluminum foil and fold it in half to double the thickness. Run the aluminum foil carefully over the can opener's blade to sharpen it. Twist the can opener along the length of the aluminum strip until you have made several successful complete blade rotations. Test the blade and repeat the process two or three times, if needed.
If the aluminum foil doesn't work, you may need to purchase a replacement blade from an appliance repair store. However, it may be easier or more economical to purchase a new can opener instead.