Volvo Repair: 2000 S80 front O2 sensor., volvo of oak park, volvo repair

Question
I've had my check engine light on for quite sometime now. I'm from Chicago as well. I took it to Volvo repair shop (Grossinger-I'm sure you know it) and they hook my car to their OBD and told me that the OBD showed that I'll be needing a new front oxygen sensor. My question is where is the front O2 sensor located at? Can you also give me the step by step procedure on how to change it. I'm pretty handy with tools and pretty much do my own repair with my car.  

Answer
what foult code did you have  ?is your s80 turbo? how many miles ? on some s 80 you have 4 o2 sensors and they are very hard to change you have to lower the catalytic converter car has to be in the air to do  it .i can give you cupon for volvo of oak park if you like %10 off labor and %20 off parts im from chicago i know volvo  gorssinger .but o2  is nothing that you can do it your self you also need special tool for o2 sensor to remove them and to try it is not worth  if you damage the cataylitic converter it is around $1100 the part.