Convert 12V to 7.8V

Hi all! I need to control a super speedy dc motor that are working with 7.8V My question is how can I get a 7.8V from 12V and then not to burn my motor. The other question is how can I win more amps because testing the motor, just with the starting it needs a lot of amps like 20A or even more! and then it stabilized in 10A, I know is really hard this motor.

My power supply is 12V but only 10A Thanks for the help David