How to change thermostat on Ignis ARL761/A fridge freezer?

Does anyone know how to remove the thermostat housing to access the thermostat on a Ignus ARL761/A fridge freezer? I have tried to take off the knob with a flat blade screwdriver but it does not come off. I cannot see any screws or places, labels, covers where there might be hidden screws. I have checked around the housing, under the bulb shield and lamp button. I'm completely baffled...

Any help most welcome and greatly apreciated.