If you see the following application load page, then your theme supports new app blocks and you are ready to upgrade.
Clicking on the Upgrade option will disable all existing vintage code installation. This prevents old code from running and reducing your site performance and means any existing sliders, image captions and Pinterest pins will no longer run/display.
Each feature will then need to be re-added as a block or section as per this article Pro Blogger: OS 2.0 Setup