How to remove cables from merten 5363 thermostat?

I am in the process of installing my first tado wired thermostat, but I am stuck at a fairly simple step. Removing wires from the existing merten 5363 thermostat. Their are no screws to loosen the wires or no clear button which can release the wires. I've tried pulling at different angles but apparently nothing works. I'm sure there is a simple way. Any tips on how to remove the wires would be welcome.
Thank you.