To stop using an account
From the Home screen, choose Settings > Mail, choose an account, and then turn Account off.
If an account is off, then iPhone neither displays the account, nor sends nor checks email from that account. You have to turn it back on to regain these functions.
To delete an email account from iPhone
From the Home screen, choose Settings > Mail, choose an account, scroll down, and tap Delete Account.
Tip: Deleting an email account from iPhone doesn’t delete it from your computer.