How to turn off two-step verification

Sorry is not possible, If you already use two-factor authentication, you can no longer turn it off. Certain features in the latest versions of iOS and macOS require this extra level of security, which is designed to protect your information.

See -> Related Article -> Two-factor authentication for Apple ID

2 Step Verification 

How do I turn off two-step verification?

Sign in to your Apple ID account page.     

In the Security section, Click Edit.

Click Turn Off two-step verification.

Create new security questions and verify your date of birth.

You'll get an email confirming that two-step verification for your Apple ID is off.

Apple ID - Two Step Verifications FAQ.  *

Are you asking about 2 step verification (Two-step verification for Apple ID - Apple Support) which can indeed be disabled, or two factor authentication (Two-factor authentication for Apple ID - Apple Support)?

Apple 2 factor authentication is required for many Apple online services (messages in iCloud, iCloud Keychain, etc) since users data for those services is stored on Apple servers and Apple is liable for the security if that data. Since “human” is notoriously careless with protecting their online service accounts that they choose to sign up for, companies have every right to insist on additional login access security settings (since companies are the ones who get sued when “human’s” data is breached).

Sorry Aprillee86 - that second paragraph was directed at iPersons, not you.