How can i remove my Audi A3 2006 halogen headlight bulbs and instal xenon bulbs?

I need to find a way to instal xenon gas discharge bulbs into my audi a3 2006 without buying a new headlight module. What kind of bulbs are best to buy and how can i do it?|||Xenons are not simple just plug and play, they need ballasts, and a different headlight assembly.