Want to sharpen you own hand saws? You do need a few special tools to do a good job.
First you need something to hold a smooth flat file perpendicular to the saw. You can buy a commercial jig for this, or make one out of a simple piece of wood as shown in the first photo. You must start every filing job by making sure that all the teeth are the same length. Any short ones will not do their job and the next tooth will take a beating. So even if it seems crazy to shorten and dull all the teeth for one short tooth, that is what is required.
Second you need a "saw set". This you will need to buy. It looks like a pair of pliers but there is an adjustable anvil on one side and a sort of plunger on the other. With this you bend every other tooth to the right or the left making the kerf that allows the blade to follow. The greener the wood, the more kerf you need. The harder the wood, the less kerf you can get away with, and hence the smoother the saw will cut.
Then you need a triangular file. The rule of thumb is that file face should be twice as wide as the depth of the tooth. This is because when you draw the file across the saw you are actually cutting metal on both sides of the groove, removing metal from two teeth at a time. If the file is twice as wide as you need to sharpen, you can rotate the file and get a good cutting action from all three points of the triangle. If the file is too small, you will wear out one pair of sides and the other two possibilities will not work. Simply set the file into the groove and follow the angle that was there before you started.
Holding on to the saw can be a bit of a problem as it won't fit well into ordinary vices, and if you don't clamp it you will have a lot of trouble controlling the cuts. You really need to clamp it close to the teeth to avoid horrible noises resembling someone learning how to play the violin. In the photos you see a professional saw vice. You can make something similar out of plywood, just arrange that it clamps just below the teeth.
For the whole story and details on sharpening any kind of saw, you should obtain the sharpening "bible" in DVD produced by Lenard Lee, available from Lee Valley Tools.