um... I guess I don't understand what you're trying to accomplish
a relay is just a switch.... you wont make the lights in a room brighter by replacing the light switch, it ether works or it doesn't
most cars will have a relay/fuse panel in the engine bay, you should find your headlight relays there if you really want to replace them, pull the old ones and find replacements that use the same voltage range and have the same pin configuration.
if replacing the bulbs didn't work then I'd go and say your next hurdle would be looking for faulty wiring/bad grounds... because if the wiring or the grounds are bad then the light isn't getting full voltage... it'd be pretty rare for a relay to cause dim lights though.