What do you want? a more powerful battery and bigger controller could provide more power to the motor if there is any room to house them but its not a machine built/designed for speed.. - any faster than a jogging pace and you need to get on the rd and off the footpaths as you could be a hazard otherwise and on the rd thats a Very vulnerable vehicle..
This thing has tiny wheels, tiny wheelbase, and no suspension. Not a good candidate for anything fast :/
How fast are you looking to go, and how fast does it go currently?