Overheating

Hello everyone, I am new to this, and I have a couple of questions. I have a 2000 VW jetta 2.0 and it's starting to overheat, and my car does not put out to much heat either since it has started to overheat. I think it's the thermostat, but I am not for sure. If ti's not the thermostat does anyone have any idea what's the problem? Is the thermostat hard to change? If not where is it and how do you change it? Any info is greatly appreciated

The thermostat is where the lower hose enters the engine block. Unfortunately water pumps are very common to break internally & cause the same symptoms.