Hi Denise, first you will have to remove the radio, put four small screwdrivers or cut the ends off a wire coathanger and put them into the square holes in the front of the radio then with a bit of juggling the radio will come out if you don't disconnect it you will not need the security code!! if you do and you have'nt got it ask a question here with the radio serial number (M123456)
With the radio out of the way you can see the back of the heater panel, the control cable might of just come unclipped or at worst the plasic splines have broken either on the cable end or the selector knob. To remove the heater panel there are two phillips screws on the top of the panel then pull the panel up and to the rear and it will come out then disconnect the electrical connectors.
If the splines on the cable end are dammaged (there is a gap in the teeth to ensure it lines up with the selected position) its a big job to replace, if the damage is on the control panel then it's a new panel (£15 ebay) and a simple fix!
nige110162@hotmail.co.uk
nigel
December 2008