After you receive the purchase confirmation email with the download link for your theme, you can upload it to your Themes page:
Your browser might uncompress the theme files automatically. Make sure to upload your theme as a single
From your Shopify admin, click Online Store, and then click Themes
Click Upload a theme in the top right-hand corner:
NOTE: You can't have more than 20 themes in your store. If you have reached this limit, you must export or delete one of your installed themes before you can install another one.
From the Upload A Theme dialog, click Choose File to select the
.zipfile that you want to upload.
The uploaded theme will appear in the Unpublished themes section of your Themes page.
To publish the theme, click Publish theme. Your current published theme will become unpublished.