That looks very similar to my motorbikes, though it's not exactly the same frame or fairings.
You will need to open it and take pitures of the controller (the big electronic box that controls the motor).
Also please take some pics of the markings on the motor.
And some information on the battery too (what voltage, what capacity, what maximum dischage current). If you don't know you can just ask the seller, they should be able to tell you. You can at least know the voltage and sometimes the capacity by looking at what's written on the charger.
Basically you are limited by one of these 3: motor, controller and/or battery. My bet would be that your limit right now is the controller, but probably the battery is a very close second since they usually fit the cheapest ones they can find. I don't think the motor will be a problem anytime soon, these QS motors can take a serious beating.
Ultimately it will come down to how much you are willing to spend, this thing can become really powerful but it isn't exactly cheap to do and the learning curve can be very intimidating at first.
You can have a look at my threads in my signature to give you an idea of the kind of things I'm talking about when I say stuff like "controller", "motor" and whatnot.
