Go to User→Settings.
Find the Two-factor authentication section and click Enable authenticator.
Open your authenticator app and scan the QR code. If you cannot scan the QR code, copy the manual key and enter it manually in your authenticator app.
Enter the verification code generated by the authenticator app.
Click Confirm. Two-factor authentication will be enabled for your account, and you will need to enter a verification code during future logins.
Go to User→Settings.
Find the Two-factor authentication section.
Click Disable authenticator and confirm the action.
Two-factor authentication will be disabled for your account, and you will no longer need to enter an authenticator code during login.