Im getting these codes for my 2002 s60:

P0036 (no signal) usually

and now P0037 (low signal).

So I know my rear o2 sensor is bad (most likely) and I am attempting to replace it myself. I just ordered the part online for about 80 dollars.

My question is, do I just get under the car and replace it? Is it hard? Do I really need a o2 sensor ratchet or can I just use a regular ratchet on it. Should I have checked my fuses before purchasing a o2 sensor? Should I download that repair software... what is it called...VADIS?

I have never done any repair to any car myself. Any input is greatly appreciated.