You bike is most likely restricted by the motor, not the controller. The only restriction you get from the controllers is sometimes they have two single wires coming out of the controller about 6" long with a small connector at the end. When joined, your restricted; when not joined, you're not restricted.
About half the small controllers I've seen have the wires. If the controller doesn't have the wires, then there's no restriction.
Assuming that there's no restriction, the easiest way to get more speed is with a 44v battery pack or even 48v. You won't have to change your controller for 44v, but it might not work with 48v.
Next, you solder the shunt about 30% to get it up to about 18 amps. You can solder the shunt with your present set-up for more climbing power, but some of the cheaper 36v 10aH batteries are a bit weak, so you might find it cutting out under full power - especially when it's running down, so don't be greedy with your soldering to try and get even more amps. With 44v lipos or a Cell-man A123 pack, you can take it to 20amps - about the maximum the motor can take.
Whatever you do, be kind to your motor. Jumping off kerbs under full power will strip the teeth on the gears, and running up long steep hills at full throttle and 20 amps can overheat the motor.