How do I sharpen the serrated knives?

Truth be told you cannot really sharpen serrated blades very easily, and there is no gadget that exists that does, but you should not need to as long as you use appropriate materials to cut your bread on like wooden boards and avoid glass and Bamboo. The Serrated edge of a kitchen knife or bread knife will last a lifetime but will not keep their sharp points forever, the serration itself will become slightly rounded in time but still be effective to use on foods that are crusty on the outside and soft in the middle, so not just bread.