To preview the new interface for yourself, just click on your name in the upper-right corner and select Try our new interface.
This will switch you over to the Learner interface. If you want to switch back to the Admin interface, click on your user icon in the upper-right corner and select Switch to previous interface.
To enable it for your learners, make sure you are viewing the Admin interface and click on Customization then on the New Learner Interface Settings button in the Branding tab.
On the following page, you'll be able to turn the interface on for all of your users. If you enable this option, the login page will also change.
However, if you want to pilot the interface with a smaller group of users, you can specify which users will have access using the Enable the new UI only for select users drop-down menu. If you go this route, the login page will not change.
Additionally, you are able to choose which widgets are shown on the Learner dashboard. Using the arrows, you can change the order in which they appear. More widgets will be released in the coming weeks.