Every six months to a year, depending on use, you should have your knives professionally sharpened. Take it to a cutlery shop—not to your local supermarket butcher who sharpens while you shop—because different knives require different sharpening tools.
These puppies just came back, and once washed and dried, will be ready again for service. That reminds me, never ever put your knives in the dishwasher—it dulls them.
Sharp knives are also safer because a sharp blade will slice easily through whatever you are cutting without much effort. You won't have to press hard or saw back and forth which increases the chance of the knife slipping and possibly cutting you. Ouch!
So go! Get those knives sharpened so you're ready for summer cooking. Your tomatoes will thank you.