Read the service manual
. It cautions against changing the carburetor jet size since this can cause problems (carbon buildup or overheating). Carbon buildup at the exhaust port is an issue; the manual recommends cleaning it out every 6000 km (4000 miles) to prevent a loss of performance.
The following discussion is based on the assumption that you are trying make the bike go faster than the factory original specifications. I did not see anything in the manual resembling a speed governor, so i assume the limits are set by the engine and transmission parameters. Aerodynamic drag increases as the square of the speed above 20 mph, so anything you can do to reduce drag will significantly cut the power needed at higher speeds.
Probably the most significant limitation to engine output is airflow through the throttle body. Increasing fuel flow at wide-open throttle will only waste fuel on a rich, cooler, dirtier burn. However, there is a maximum amount the cylinder can pull in, so simply installing a larger carburetor may produce only a limited increase in power. Forcing more in (as in supercharging) risks an over-pressure condition and blown engine.
In the ignition system, capacitor charge time may be an issue at higher RPMs. You can decrease this slightly by replacing the diode with a silicon carbide diode (make sure it is rated for the same or higher voltage and current as the original diode). Also, make sure the connection between the magneto coil and ignition circuit is clean and solid. Likewise, check the ignition coil connections to make sure they are good (the manual lists the resistance for the standard coils; you want this as low as possible. Ultimately, the inductance of the ignition coil limits the charge rate, but this cannot be reduced without problems getting an adequate spark. Otherwise, do not try to bypass the capacitive discharge ignition; that's the output of the timing control.
Speaking of timing, higher power engines will typically advance the spark at higher RPM to ensure combustion pressure starts rising at top dead center. Unless your ignition magneto has a centrifugal stator advance mechanism, your engine probably has fixed timing. Modifying this is a tricky business; if you fire the spark too soon you will lose power and risk damaging the engine with detonation.
The maximum RPM shown on the spec sheet is 5000. Exceeding this can damage the engine; the lubrication system may not be able to keep up with the demand for oil flow, and centrifugal forces may exceed the strength of the metal. If the engine throws a rod at high speed, you could easily get hurt. The only way to go faster than the design speed without exceeding the engine speed limit is to install a transmission with a higher top gear ratio. But if you do this, you may find your brakes are inadequate for emergency stops at this speed.
I suggest you would be better off saving your money for a bike designed for higher speeds rather than risking this one on potentially hazardous and damaging modifications. In some jurisdictions, it is illegal to travel over a certain speed (typically between 25-35 mph) on moped or scooter class vehicles.