Before I begin, let me say that I am a newbie. I have never made a car repair in my life, i don't even know where my oil filter is in this car! So I really need your help.

My 92 525ia is overcooling. So I have to replace the thermostat.
In looking on the web, it seems that the procedure is pretty simple.

So I went to BMA and found the stat that fit my engine.
What's the difference between a 95 degree, 90 degree, and a 78 degree stat? Which one should I buy? Do I just buy the stat or do I need other stuff?

I live in North Carolina, in a region that sees 3-4 snows a year and highs in the summer reach the 90's.

Thanks Guys!
-ashley