As much as we’d love it too, the core structure of the PRO themes has too many differences to work as an upgrade of the Lite versions. What you need to do is to install a fresh theme with the PRO files and start customizing it with the newly available structure.
Keep in mind that all your posts, pages, pictures, custom posts, and most of the customizer options will already be there while you switch the themes, but there might be a few small differences in design. The switch to PRO shouldn’t take more than an hour to replicate a fully built Lite theme inside the improved theme.