You control the temperature in your room with the knob on the radiator. Some houses/rooms have thermostatic knobs on the radiators. If you set these to setting 3, the temperature in your room will be around 20 ºC.

Are you going away for a longer period of time?
Then set your heating to a lower setting, around 15 ºC is a good option, so it doesn't cool down too much. That way you won't burden the environment unnecessarily.