How do you replace a heater matrix on a Peugeot 307?

To replace the heater matrix on a Peugeot 307, start by draining the coolant from the system. Next, remove the dashboard to access the heater unit, which involves taking out various trim pieces and possibly the center console. Once you have access, disconnect the hoses and electrical connections, then unbolt the heater matrix from its housing and replace it with the new unit. Reassemble everything in reverse order, refill the coolant, and check for leaks.