02 Trailblazer Thermostat Replacement

My 02 LTZ is not heating up at all and its cold here in NY. I replaced the clutch fan yesterday because I thought that was the problem; seeing how they have a bad reputation. But it still only gets up to 100 maybe 120 degrees. I suppose now I will go out and buy a $36 thermostat and replace that. Any other suggestions on why this may not be heating up? And any suggestions on how to replace the thermostat. I see that is is located in the driverside fender well. This ought to be fun to replace. Need some help please.

Sounds like a thermostat issue, but appears to be in the housing where the upper hose goes into the block next to the p/s pump.