Before you can mount tado° onto your radiator, you will have to remove the existing radiator thermostat head. Unmounting depends on the type of radiator head:
Some of the thermostatic heads can simply be unscrewed from the valve body. Be careful to open the head screw nut and not to turn the full head which will unscrew the valve fitting itself.
When you see that the head is fitted by a screw, please remove that one first and then pull off the thermostatic head to the front.
A few thermostatic radiator heads are removed by turning the head beyond the maximum temperature setting. Be careful to only unscrew the head and not the valve fitting itself.
If none of the above seems to fit your thermostatic radiator head, try simply pulling the head off. For those cases the head usually consists of two parts and you will have to remove the component beneath to which the head itself had been mounted.