Probably have to replace the motor, too, once it overheats from the extra power, and damages the windings or melts the wires in the cable together and shorts the controller out (blowing it up).
It is probably not limited by something in the controller, but by the total power required to go faster.
What speed does the wheel go when it's off ground at full throttle?
If it's exactly the same as when you're riding it, then the controller is still locked, and you'd have to replace it and your display, etc with one that isn't. (depending on how customized they made the system, you may have to replace everything inlcuding the battery, as some systems won't work with any parts other than factory stuff).
If it's faster off ground, then you're limited by power and voltage, and you'd have to replace the battery, controller, display, and probably motor, to fix that.
It's almost certainly a lot cheaper to buy a vehicle designed for the speed and usage you have (these small-wheel kickscooters weren't intended for those speeds even when they are advertised as capable of them)