There are a couple of ways you can set this up. The simplest option is to hit this link and follow the steps.

Or, you can update your settings manually. All you need to do is:

1. Login to your account 
2. Click your name in the top right-hand corner 
3. Select the ‘profile’ option 
4. Scroll down to the security section 
5. Click ‘Update your 2 factor authentication details’ and follow the steps