1. Open your Google Account.
  2. In the "Sign in & security" section, select 2-Step Verification. You might need to sign in.
  3. A pop-up window will appear to confirm that you want to turn off 2-Step Verification. Select Turn off.
  4. Destroy all the backup codes that you've saved for signing in to this account.

For more information how to turn off 2-Step Verification for Google Accounts, please refer to Google Help Site.