How do I change an O2 sensor 1 bank 1 before cat in an Audi A4 quattro 2001 V6 2.8L?

Im trying to do this my self and I can see the o2 sensor I just can't reach it and I need to know what to remove to get there. THANK YOU A LOT!!!How do I change an O2 sensor 1 bank 1 before cat in an Audi A4 quattro 2001 V6 2.8L?Have an exhaust shop do it, or a mechanic. This is not a job for a DIY'er.How do I change an O2 sensor 1 bank 1 before cat in an Audi A4 quattro 2001 V6 2.8L?How do you know it is defective ? Did the code from scanning say it was defective ? Usually the code will state a problem to diagnose and the O2 sensor is only an indicator not the problem.

NEVER replace any part till yoy KNOW the problem.