How do you change the engine thermostat on your astra 1.7 cdti 07?

To change the engine thermostat on a 2007 Astra 1.7 CDTi, first ensure the engine is cool and disconnect the battery. Drain the coolant, then remove the necessary components to access the thermostat, typically located near the engine block. Unbolt the thermostat housing, replace the thermostat with a new one, and reassemble everything, ensuring all seals are secure. Finally, refill the coolant, bleed the system of air, and reconnect the battery.