Make a 50cc scooter more powerful?

The easiest most cost effective way to increase your scooter power is with a big bore kit. There are dozens of companies that make them. Polini and Hoca are popular companies that make quality kits. Just make sure you increase the jet size on the carburetor or else you risk running too lean fuel mixture ration and overheating your engine. I would not waste my money on an exhaust. The biggest bang for the buck is a big bore kit.