Knives that have serrated edges typically require special grinding equipment. Stainless steel blades are best done with diamond-coated stones.
For non-serrated edges, a relatively inexpensive sharpening kit is made by a company called Lansky. It consists of a jig that will hold the blade and then allows you to select one of 3 sharpening angles 5/10/15 degrees (I believe). You won't be able to use the stones with the kit (they are for carbon steel blades), you will need to purchase the diamond stones separately. (not cheap). Attempting the sharpen stainless steel blades with non-diamond stones is a complete waste of time and usually results in making the edge duller by the time you are done.
You can also purchase a round diamond sharpener to sharpen the serrated portion of the blade. But it is done by hand and usually only successful if it is just "touching up" an edge. If you attempt this, read the instructions very carefully. Sharpening is not lengthwise along the edge, as it would be with a straight edge.
For dull edges, I would recommend sending the blade/knife in to the OEM for sharpening or replacement. Or find someone locally who knows what they are doing.
All in all:
Lansky kit: $45
Diamond hones (need at least medium and fine) $45 ea.
Diamond round (for serrated edge): $30
Unless you have a lot of knives, it's usually not cost-effective to get the setup.
Serrated edged knives look "cool" and have some nice qualities, but lately, I have gotten completely away from from because of the difficulty sharpening them.
I also have gone back to good RC60 carbon steel instead of stainless, a much better edge can be put on them.
