Dear Soumitra, you cannot change the photo background. You can only upload a new photo with the required and instructed background. The first thing is you need to change your photo only if you received a notification at your registered Email or phone number asking you to change those details. If you haven't received any such notification, you needn't make any corrections and you can leave them the way they are right now. Login to your credentials and click on the button which says " Click here for corrections in the NEET 2019 Application". Make the necessary changes like updating the photo and signature accordingly. But if you are unable to make any changes ideally it is because you haven't received any notification and your images are good to go!