What is the correct way to sharpen a chain for a chain saw?

Use the correct round file and use a jig that clamps on the bar. This allows you to set the right angle for the chain. Also after sharping the cutting teeth. Then you need to knock down the piece in front of the cutting teeth or you won't cut chips out as the cutting depth will be too low. What round file is right? Ask the small engine shop near you they will be able to help you. I always just buy extra chains and just change them out. Then take the dull ones to a sharping shop, the cost is worth no hles. Good Luck