How to change DOB in birth certificate?

Hello everyone.. I am in need of help. My problem is I need to change DOB on birth certificate. In all my records DOB is given as 15/07/1973 but in my birth certificate it is 18/10/1973. Now my question is: Can I change the date in birth certificate as 15/07/1973 or do I have to change in other certificates? What are the procedures and how long it will take to get everything done? Any help is appreciated.