Change Termostat Xedos 6 2.0 V6 1995
 

Where is the Termostat located?

Do you need to take out all of the cool liquid?

Between the 2 zylinder heads on the gearbox side of the engine.

Depends how you want to work.
If you just open the case of the termostat then some of the coolant will come out.
If you don't want this, drain a little bit at the bottom of the radiator or somewhere else.