Engine Overheating Options

[Araykhel]

I have an ST204 that just crossed over 107k miles and I'm having some overheating issues after the car has had about twenty minutes of drive on it. When my car is driving at normal speeds my indicated temperature usually sits at half, great and normal . But once I let off the gas and decelerate the temperature climbs in no time. I find that idling is the worst and my temperature sits just below the red line when I do so.

I've used the great and nifty search feature to educate myself on all the issues to check/ possible fixes however I still have some questions. The first thing I want to check/ replace is my thermostat however I tried searching for a how-to assuming it wouldn't be a simple swap and found none. Do I need to drain fluids ( ) to do so?

[Bitter]

IIRC the bimetallic valve is for the evaporative emissions system.