Take it to any garage/shop/dealer/halfords and theyl do a antifreeze test for free or a very small charge, If youve none in then if you look at were the 2 water hoses go into the heater matrix (right hand side at the rear of the engine) Youl see the left hose has a bleed cap on it. Just unscrew it the cap along with the radiator cap and let a litre of water out. retighten the top up radiator with a liter of pure antifreez and the jobs done. If youve got any doubt just take it to the dealers and get it done as a frozen engine can run into thoushands to put right