The uploaded theme appears in the Unpublished themes section. You can install a maximum of 20 themes in your store. To publish the theme on your online store, click Publish theme. Your current published theme will become unpublished.
And you can click the "Actions" > "Publish" to publish the theme. A published theme is the theme that customers see when they visit your online store. Your published theme appears in the Current theme section of the Themes page, and your unpublished themes appear in the Theme library section. If you publish a new theme, then your previously published theme moves to the Theme library section. None of your theme changes are lost.