1998 S Reg Heater Thermostat Replacement

[tftisme]

Can anyone advise me if there is an easy way to replace the thermostat for the in car heater? Mine is constantly blowing out freezing cold air despite being set to the maximum, make me toasty setting, i'm guessing the thermostat is either stuck of knackered.

I've had a look in my trusty Haynes manual and it says i have to remove the alternator and take note of the route of the timing belt - eek, I'll tackle most things but really don't want to mess with the timing(have visions of wrongly routing it and ruining the valves).

Any advice or help would be great as I'm getting a little fed up with scraping ice off the inside of the car as well as the outside.

Thanks