1. On the iPhone or iPad home screen Tap the Settings App.
   
   
2. Scroll down and tap "Accounts & Passwords" or "Mail, Contacts, Calendars" if you're on an older device.
   
   
3. Under accounts you should find the old email account you wish to remove, tap on it in the list.
   
   
4. Uncheck every option under this account to keep the details there but disabled in the mail app.
   
   
5. Once Disabled you can delete the account later if required.