How can i get a code for my immobiliser Renault Megane?

i have a 5dr renault megane, my immobiler doesnt open the doors and doesnt start the car untill i put in a code using the central locking button from inside, when a light goes off on the dashboard i can then continue to start the car, but i have to do this everytime i want to go out in the car, is there any way i can re-code this to make my key work. i really dont have a clue abouty this stuff.. any help would be kindly apprecitated