The new 2.60 version of Open Atrium includes a brand new theme. By default this theme is only enabled for new installations. To use this theme on an existing Atrium site (upgrading), you need to perform a couple of extra steps:

1. Go to the Drupal Admin -> Appearance page and click "Set as Default" for the "Open Atrium Modern Theme" (oa_theme).
2. Under Core addons (Details - then: Enable App) enable the "Open Atrium Site Layout Defaults" module (oa_site_layout_defaults). This should also enable the dependencies: oa_site_layout and panels_everywhere.
3. Clear Cache.

That's it! Now you should see both the new Modern theme (distinguished by the Green header) and all the new admin widgets that are part of the Modern site layout defined in Panels Everywhere.

NOTE: If you don't see the green toolbar, go into your Appearance -> Colorizer page and check the location of the colorizer.css file. For the new theme it should be assets/css/colorizer.css instead of the old assets/stylesheets/colorizer.css that was used by oa_radix.

You can change the site layout easily via the Structure -> Pages -> Site Layout panels page. Just create a new Variant for your layout. The Modern Layout is triggered by using the oa_theme Theme. You can set up your own selection rules and support several different layouts. If you want to go back to the default layout but keep the new theme, just disable the Modern layout variant.