To get more power, you simply buy a battery with more voltage. However, you need to ensure your vehicle and it's
electronics can handle the extra power to avoid damage.
Typically you can find this information in your user's manual, if you're unsure just ask us - never guess!
It's not too uncommon that to install a battery with more voltage that you need to modify the RC car in someway,
this may include installing a different motor gear, cooling fan and even change your driving style.