If you purchased your theme directly from the Out of the Sandbox website:
Our Theme Updater App now includes the ability to install a fresh download of the most recent version of your registered theme. This feature is available for all plans (Basic, Pro, Expired/No plan). You do not need to be on a subscription plan in order to obtain a fresh download of your theme, just follow these steps:
Step 1: Install the Theme Updater App
Step 2: Register your theme
Step 3: Within the Theme Updater App, click the 'Actions' button for your theme and select the 'Install Default Theme' option from the drop-down menu:
Step 4: You can type in a new theme name and click the 'Install' button.
This version will contain only the default configuration with no customizations. It will be installed as a new, unpublished theme in your shop.
Note: If you happen to still have your original order confirmation email containing the download link, you can also use that to download a default theme file.
If you purchased your theme from the Shopify Theme Store:
If you bought the theme through the Shopify, then you can also visit the Themes Store while logged into your Shopify account (must be logged into the same shop that you originally purchased the theme), locate your theme, and click on Add latest version.
The blank theme will be added to the Themes page of your Shopify admin.