I would advise that you change the coolant. As previous posters have said this is a job to be done every few years. Get down to the local library and get a copy of the relevant Haynes manual - or photo-copy the relevant pages for specifics.
Generally though: When the car is cold; look for a drain plug at the bottom of the radiator before you go disturbing hoses. Undo the header tank cap, get a tray under the drain plug and loosen it so the coolant flows out. When the flow has ceased, tighten up the drain plug. Mix up the relevant proportions of anti-freeze and water and pour it VERY SLOWLY into the header tank until the 'max' mark is reached. The reason for pouring slowly is to minimise the chances of airlocks in the system. Cover the header tank opening with a cloth and start the car and run it up to operating temperature - when the fan cuts in turn it off. Whilst running up to temperature avoid the urge to 'encourage' it by blipping the throttle. Also whilst running up to temperature, top up the header to 'max' as needed SLOWLY. Having reached operating temperature and been turned off, leave the car to thoroughly cool down - ideally over night but at least for a good few hours. Remember that anti-freeze has a 'seeking' action especially a new mix so check for leeks. Once the car has cooled down, top up the header as necessary (SLOWLY) and give the hoses a squeeze or a tap to loosen any remaining trapped air. Finally replace the header cap and take for a test drive, return home and check for leeks. Whilst on the test drive put the heater on - if you only get cold air with the setting to hot then you've probably got an airlock - back to ticking over with cap off and squeezing hoses etc. Long and boring but worthwhile.
Best of luck
