Multi-Factor Authentication (MFA) is a form of security that requires a time-sensitive generated code every time you log in.
To manage your MFA settings on your StellarX account you will need to go to your Account Settings.
Your Account Settings can be found in the drop-down menu under the profile icon in the top right of StellarX, just to the left of Deposit and Withdraw buttons. From there navigate to the 'Security' tab and you should see the 'Multi-Factor Authentication' option there.
To enable MFA, click on 'No multi-factor authentication'. You will be asked to scan a generated bar code from StellarX using your MFA app of choice (i.e. Google Authenticator, Authy, etc). The app will then give you a 6 digit code to enter in StellarX.
Once this is done your MFA should be set up and good to go, you will see the selection turn to 'Require multi-factor Authentication' and a list of your remembered devices, which you can remove at any time. Each time you sign in on Web, you will need to enter the generated code form your MFA app.
To disable MFA, click on the (now un-highlighted) 'No multi-factor authentication'. You will be asked if you are sure you want to disable multi-factor authentication. If you would like to proceed click 'Confirm', otherwise hit 'Cancel'.
For all the options you can find in account settings please see This Link.