I'm just beginning in electronics, but from what I have seen so far, a step up transformer should change six volts to twelve volts. You just get half the amps.

I'd steer clear of it unless you work in electronics and have access to the wire, other components and expertise.
Many years ago, I rewired my old Lambretta and simplified it right down to just a few wires, I ended up rewinding one of the magneto coils to cure an intermittent ignition problem.
Automotive electrics are simply pants.
Del