how do you change a rear tail light bulb on a 1996 golf?

I have a 1996 volkswagen golf that needs a new tail light bulb. I want to know how to get to it and replace it. I also, think that I need a new oxygen sensor. Any ideas on how to replace that? Thanks!

The tail light bulb holder assembly pops out by depressing the plastic clips. The bulbs are the old style 1/4 twist & pull out. If it needs an O2 sensor it would set a diagnostic code indicating it. The car is OBD-II so any generic scanner could read it. Autozone & Advance Auto will usually scan for free. O2 sensors are usually 7/8" & simply bolted into the exhaust, one before & one after the catalytic converter.