Every theme you load into the /themes folder of your /motif-enabled template will become an option to use as a theme on a particular page, or on all pages. To set a particular theme as the primary (default) theme for all pages, open your template parameters from the Template Manager. In the "Primary Theme" dropdown menu, choose the theme you'd like to make primary. All subfolders in the /themes folder of your /motif-enabled template will appear as an option in this dropdown list.

Note: Your /motif-enabled template must be set as the default Joomla! template or assigned to particular Joomla! menu items for a /motif theme to appear on the front end.