I've had mine from new and (touch wood) never had a problem with the central locking or the alarm apart from the battery going in the key itself so first of all check the remote function on the key is actually working by seeing if the red LED light flashes when you press the button. If the light is'nt flashing it my be the case the battery needs changing. At the top edge of the key there is a small slot which you should be able to prize open with a thin coin or small screw driver. Inside you will see the battery which is a CR2032 (like a watch battery) which you can buy from somewhere like Jessops or even larger Tesco stores. You also may wish to check the appropaite fuse which is F38 which is located in the dashboard fuse box. To be honest, I cannot think of a reason the remote function on the key would need re-programming to operate the central locking and alarm unless the car has had electrical issues in the past.
