The sharp edges on your router bits need sharpening after a while, as any blade does. If the router bits aren't sharpened, it will become harder and harder to cut wood on the router and the bits will eventually need replacing. Diamond abrasives are the best tools to sharpen router bits. It may help to have two sets of router bits so you can change out any dull bits immediately and sharpen them at the best time.
Hold the carbide bit in one hand while holding your diamond paddle or file in the other so you can scrape the paddle/file against the flat radial face of the bit's flute. It can be possible to keep the bit mounted within the router collet or workbench, if that is what's more comfortable to you.
Apply five to 10 strokes from the abrasive surface to the surface of one flute, going along the entire edge. Turn the bit around and give the same number of strokes to the other flute. Repeat this process to sharpen the bit evenly.
Feel the bit carefully and view it under a strong light. Look for flecks of light along the edge. If there are no flecks and the edge has a sharp feel to it, it should be fine.
Clean the bits at the same time that you sharpen them, maybe more often. Remove the ball bearing pilots from the bits, apply non-caustic bit or blade cleaner and let the bits stand for 10 to 15 minutes. Scrub them under warm water with a toothbrush and let them dry.You may need to clean the bits daily if you use them on pine or other woods that have resin.
Apply a coat of water or light oil to the surface of your diamond paddle or file. This will extend the life of these tools, as it prevents them from clogging and reduce the number of times you need to clean them. Use diamond abrasives that are either fine or extra fine---between 600 and 1200 grit. Hand sharpening with anything coarser can fracture the edges, and router bits that that would need those types of abrasives should be professionally grinded.