First, in your Vend Ecommerce store, navigate to the Design – Themes menu.
Select the “Upload Theme” button at the top and accept the Terms of Service. Then click “Upload Theme” and select the zip file of the theme you are trying to install.
After this, Vend will display a message notifying you that the theme is being uploaded. Wait a few moments then try refreshing (Press F5) the page. Your newly installed Theme should be in the Themes List