I need to bring 12v down to 6v please help.?

I have a moped that runs 12v and I got a bullet head light and its a sealed light bulb that is 6v I need to bring it down to 6v before the bulb so it doesn't burn out someone said a step down transistor but I don't know please help to tell me how to do it I don't need to bring down the whole system volts just something before the bulb