How to Upload a Shopify Theme Using a .zip File
If you purchased your Shopify theme through a third-party such as Out of the Sandbox, Pixel Union or Envato Market, you will need to know how to upload a Shopify theme using the .zip file you purchased.
Go to your Shopify admin and click on Online Store. By default, you’ll be brought to the Themes page.
Click on the Upload Theme button under Theme Library. Choose your .zip file and click on Upload File.
To activate your new theme, click on Actions and select Publish.