How to upload business assets to use in a theme
By default any asset related with a theme is remove when a new one is uploaded (even if the same theme).
From the app you can upload images that will be treated as personalized images and will not be deleted with each new update of the theme.
To upload a file you must go to “Themes / Assets” and click on “Upload Asset”. Once you upload the file you can click on the file to get its url. Copy and paste that url where you need it.