Kelton Hollowing tools Sharpening?

I have just purchase a set of Kelton Hollowing tools,with three tools, curve, straight and slightly curved. They fit into a large metal handle and held in place with set screws. I was wondering how do I sharpen these tools. The end are made of heavy steel with an end shape like a scrapper. I have two or three diamond pads but I am not sure how to sharpen. Any suggestions -- Harry