In principle, you can use any standard Chinese controller because they all work the same. We recommend a KT sine wave controller with LCD and the rest of the stuff from PSWpower.com. You will need to tick the 10 pole PAS, thumb throttle and speed sensor as well as the LCD3 when ordering. Cost is about £70. get the 36v/48v one in case you want to go up to 48v when your battery expires. You also need a motor cable extension.
You have to disassemble the present controller from the battery base and run some extension battery wires to wherever you locate the new controller. Decide how and where tou want to house the new controller. Easiest is in an under-saddle tool bag. Cut the motor extension cable 8" from the end with male pins, cut off your motor connector and join the two wires. Cut off the motor connectors from the new controller and and join the wires from the other length of motor cable. Install the throttle, LCD and pedal sensor. connect everything up and enjoy your new system.
Brake switches are optional. I can't remember if your bike already has them. if it does, splice in the wires to the controller. personally, I don't use them with these controllers. The speed sensor is just in case your motor's one packs up or doesn't like to play.