how to remove gamil account
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how to removed gamil account
<Personal Information Edited by Host>
iPhone 5, iOS 6.0.2, null
To remove an email account, go to Settings>Mail, Contacts, Calendars and tap the account you want to delete. Tap "Delete Account".
I suspect that's actually not what you're asking though. If you're trying to reactivate a phone and it's requesting a passcode, you need the passcode to the Apple ID (which could be a gmail account) in order to do anything. If the Apple ID is yours and you've forgotten the passcode, start here:
If the Apple ID is not yours, unless you can get the original owner to remove the phone from their account, the phone is useless to you.