Where do I find the thermostat on a Vauxhall omega 2.5 1997?

My car is overheating. I checked the engine and found that on the right side of the radiator pipes, they were hot while the opposite side was cold, this leads me to believe that the thermostat is sticking and probably needs repairing. I am going to change the thermostat but I need to locate its position can you help.

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