Search the site there're loads of posts about this.
You can either upgrade just the bulbs Phillips Xtreme or Osram night breaker seems to be the favs, or HID conversion the other and really less effective way is to mod the lights i.e. wire them so they are both on at the same time. This latter option is not the best way and is a trade off as you have to readjust the highbeam so as not to blind on coming traffic as the reflector is made for highbeam pattern only, so you lose your highbeam.
The reflectors is where the problem lays there shite.
The last and best option is to get hold of a 400 headlight unit these are both H4 and high/low beam reflectors, stick in the bulbs above and 100% improvement, convert to HID and wow. Problem is these units are like rocking horse pooh!!!!!