Your Gmail id is your Gmail - the actual email-account. It cannot be changed. You can of course make a new one, but you cannot change the actual email of an existing account. Unless you're talking about something else, but then it's not your Gmail ID.
I heard digitalpoint can take my ip then , if i create another a/c they will ban me for life time. now what should i do?
Do you mean you want to change your email address on the forum? If so you do it here: https://www.digitalpoint.com/account/contact-details
lol, now I know why you initially posted this in "site and server administration" thinking it was referring to this website. Still not sure why the thread title is "security" though. Just go into https://www.digitalpoint.com/account/contact-details and update your email address.