Hi,
The skin will become available as a download in ClearPass in the same way software updates become available. Install the Skin once downloaded. Now you need to enable the skin.
This can be done globally so it becomes the web admin interface skin and the default skin for any new guest/onboard pages. To enable the skin on pages already created you'll need to go to the page within ClearPass and select the skin you want from the dropdown list.
Cheers
James