If you have many galleries uploaded to your web server, you can have them all share a single instance of the 'jbcore' folder by following the instructions here.
When a new version of Juicebox-Pro is released, you need only replace a single folder on your web server to upgrade all your galleries at once.
If you have made any modifications within the 'jbcore' folder (for example to the 'theme.css' file), then these modifications will need to be applied to the new version of the file but since Juicebox-Pro was released, we have added many configuration options (in v1.2.0 and v1.3.0) which can now be set in the gallery's XML file (such as control over shadows and the gallery font) which were previously only achievable by modifying the 'theme.css' file.