headlight troubleshooting

[miahshodan]

I just bought a 2012 A6 3.0 premium plus. One of the Xenon headlights has a cracked lense and is burned out. Neither Hi or Lo work. But the LEDs and signals do.
My questions are:
1. I plan on replacing the housing, but does anyone know if I need to replace ballast or bulb or both?
2. can I troubleshoot them by moving the bulb or ballast from the good side to the other?
3. do I need to remove the bumper cover to remove the headlight housings and if so, are there instructions out there?

thanks!

[miahshodan]

Here is what I found in case it helps anyone in the future:
*The ballasts are the same on both sides, so I moved the one from the good side to the bad side and the headlight worked so I knew the ballast was bad. I did the same with the bulb first, for good measure.
*Evidently there is just one bulb and ballast for high or lo.
*Yes you need to remove the bumper cover and wheel wells to replace the housing. It is a pain, but not as bad as I had feared.