How do you replace thermostat on VW Fox?

To replace the thermostat on a VW Fox, first ensure the engine is cool and disconnect the battery. Drain the coolant from the system, then remove the hoses connected to the thermostat housing. Unbolt the housing and replace the old thermostat with a new one, ensuring the rubber O-ring is properly seated. Reassemble everything in reverse order, refill the coolant, and check for leaks.