want to have a new name

My brothers name is Girdhari Singh.  He has completed his MSc. i,e  He has done PG.   In all his certificates and other legal documents for eg pan card, driving license and voters id  his name is Girdhari Singh.    Now he want to change his name and want to be named as Saahil Singh.     How it is  possible? what are the procedures?                                                Anticipating correct answers from you.  Thanks, Please give me correct answer.