The following article will take you through the process of removing your email address from your IOS Device (Phone/Tablet)
Step 1) Go To Settings
Step 2) Tap on Passwords and Accounts. In older versions of iOS this might be called 'Mail' or 'Mail, Contacts, Calendars'.
Step 3) Select the email account that you wish to delete
Step 4) Tap Delete Account at the bottom of the screen
Step 5) Confirm by tapping Delete Account, or in some cases Delete from my iPhone