How do I turn off two-factor authentification?

Two-Factor Authentication cannot be turned off. There was a time for older accounts that would give you 2 weeks to shut it off after you activated it, but currently two factor authentication is required. The relevant text from the article viewed on the top of this page is:

If you're already using two-factor authentication with your Apple ID, you can't turn it off. If you updated to two-factor authentication inadvertently, you can turn it off within two weeks of enrollment. If you do, your account is less secure and you can't use features that require a higher level of security.