Unless you’re an iPhone wizard, it’s sometimes easier to delete your IMAP account from your iPhone and start over rather than trying to edit settings.  Here’s how you do that.

Tap Settings.  You will find this on your home screen, most likely.

Scroll through settings until you find Mail, and then tap on that.

Tap on Accounts.

Tap the account you need to delete.

Tap Delete Account.

That’s it!  Please see our post on setting up a new account to start again.