Hello aspirant,

You need to go to the court and get a affidavit done to change your name. As for the board certificate, it is suggested that you change it before appearing for the boards and not after. You need to contact your school for it, and it will be done but fine will be charged. 

To change the name in your certificate after ICSE, it will be a lengthy process and you will need a good advocate. If you don't change your name in the certificate, it will create problems at places where the class 10 boards certificate is needed. All the best!