How to fix the heated blower in a Ford Mondeo?

Hi, I have a Ford Mondeo (96 P reg) and can't get the heated air blower to produce warm air! The blower fan seems to be ok, getting a good blast of cold air on all positions.

I've noticed that the control knob for the heater doesn't actually move smoothly from hot to cold and vice versa. I guess I should remove the knob itself to see if it is actually turning the mechanism behind it. However, I am unsure as to how I should remove the knob and don't want to just pull it off if its not supposed to be done like that!

Does anyone know how to fix this? A bit of information on the type of heater system in use and any dismantling instructions would be very much appreciated.

Thank you.