how do I make my dim headlights brighter

Try a headlight restoration kit, by 3M or Turtle Wax, for example. There is a cleaning solution and sealing solution that make the lenses of the headlights clear again. This may help significantly. The other option of course is to replace the bulbs.

Most headlight restoration kits I have used only last a few weeks til the lense becomes cloudy again. Duplicolor headlight restoration kit includes a thin clear coat spray paint that works well to keep the lense from oxidizing again after you polish it. You can also get new brighter headlight bulbs. I recommend Sylvania SilverStar Ultra bulbs. They are much brighter and whiter than typical headlight bulbs.