Good question! Thanks for bringing that up.
License keys are a new feature that we began to roll out on all themes.
You will be able to enter your license keys under Appearance / Theme license menu settings and activate it.
This will allow you to use the auto update feature which means future versions can be installed easily with 1 click from the Themes admin page.
Please locate the license key to the individual theme and add it on your site in Appearance / Theme license. After that if there will be a new theme version available you will be notified in the WP admin.
We put this in place to make updating easier so you do not need to use FTP or your hosting control panel / file managers and remove the old versions, then update the new. It will work with just 1 click.
Next week we will finish up the integration for all themes and I will put together a full guide regarding this.
Hope this explains it.