Thank you very much Pranathi for your reply, Could you suggest at present what I have to do.but the problem is I am writing now 12 class exams, and also I have to appear for NATA.I have noticed after one plus year. Is there any other solutions to resolve my problem.any problem for higher studies in abroad 

If you are student of cbse board, it will take a span 15 days for your surname to get changed. But if you are student any state board of the country it will take a time of 1 month.

Plan in such way that it wont stop you from attending NATA. If you have enough time please write a letter to higher authority of the board and prepare a notary affadivit immediately. So that it won't effect you from attending NATA.

thanks once again pranati onc eagain for your valuable reply,Iam cbse student of 2017 passed out and at present iam persuing in state intermediate board of education from telangana in plus 2. exams are going to held from 28 th february and it will be complete on 13 th march.i have appreared  JEE mains paper2 and i acheived 94 percentile. ihave given my name as per passport surname chilakamarriNow iam plan to appear for NATA which is going to held form april 19. i have passport with the surname of chilakamarri and valid US visiting visa of 10 years. and i visited US in the month of May 2017 and i hve been there for one month, just visiting. But to apply for GRE surname of passport is consider or 10 th class memo surname. if they consider the 10 th marks memo surname then it will be problem.i have spoked to CBSE regional office chennai branch, they said i have to get a farwading letter form school stating the correction in surname , and self declaration letter satating the same, after sending the letter they will intimate through amemo stating what further is to be done.   

So you have more than a month time for your exam so it is better you send the forwarding letter as fast as possible.

For GRE there is no requirement of 10th cerficate. But they may ask for it when you join a job. Hence if you make necessary correction now. It will be helpful for you.