1. Faster motor
you can install a motor that has higher RPM's than the stock motor. this is pretty easy swap, the hard part is finding a motor with the higher rpms, but is the same size and most only go up a few hundred rpms ( i.e. 2750 rpm to 3200 rpm) so the swap wont gain much. so even if you swap out your 250 watt motor for a 500 watt motor that doesnt mean it will go faster, just means it will get you to top speed faster(it also means you need a new controller to handle the higher wattage too). motors have a top rpm for there voltage rating. swapping a lower wattage motor to a higher wattage motor doest mean it will spin faster. look at the specs.
2. Sprocket swap
swap out the stock sprockets. lets say your scooter has a 11t motor sprocket and a 75t tire sprocket. change the motor sprocket to a 13t and the tire sprocket to a 65t or 55t or as low as you want. the disadvantage is you lose torque when you do this, you may get top end out of it, but you lose take off speed in the begining. the other con is if you go too low, the scooter motor may not have enough torque to move you faster, meaning you may have the gearing, but the motor is not strong enough to go faster.
to over volt you need three things
1. extra battery or batteries, the same amphour as what is already in you scooter (and roughly the same age as the other batteries so you dont put old batteries with new ones)
2. new controller, because with more voltage the old controller wont work now. the voltage must match the controller rating, so if you are going from 36v to 48v you need a 48v controller. same goes if you are going from 48v to 72v, you need a 72v controller.
3. SPACE, and i guess this is a big one, because if you dont have space to add this stuff, the point is kinda mute on modding your scooter. DO NOT OVERVOLT THE MOTOR MORE THAN 1 1/2 TIMES THE RATED VOLTAGE IF YOU WANT YOUR SCOOTER MOTOR TO BE RELIABLE.
Speed, Distance, Torque... Pick any 2