There is a very easy way to sharpen your rotary shaver blades. The only item you will need is a ceramic mug. By using the ceramic mug bottom, you can sharpen your shaver blades easily and very quick in about 10 to 20 seconds. Below is a video from YouTube that shows you how to do it. There are also screenshots of the videos if you don't want to watch the video.
How-to YouTube Video by niacal4nia
Take out the shaver head from the body.
Take out all the shaver blades.
Separate the shaver blades from it's casing.
Put back the bladeless shaver head back to it's body.
Place the shaver blades without it's casing back to the shaver head.
Place them carefully so that they won't fall off.
The the bottom of a ceramic mug and press against the shaver blades.
Turn on the shaver for ten to twenty seconds. It should be long enough to sharpen the blades using the ceramic surface.