Freezer Thermostat problem - Scandinova FF6745D?

How do I replace a freezer thermostat on a Scandinova FF6745D? Freezer is meant to be frost-free, but is now constantly over-freezing at the bottom (bottom draw gets stuck in due to ice underneath). The fridge section seems to be working fine. Temp. display at the top of the unit is showing -40C - so presume that the thermostat is bust.

PS is there a separate fridge thermostat somewhere? Has anyone got a maintenance manual for this unit?

Thanks