Is it possible to upgrade my Style Guide from v1.3 to 1.5? If so, how?
I would make a duplicate of the project first, and maybe a backup too (cmd + s when in designer).
I would then try this video that walks you through how to add Relume to an existing project - which in this case should be the same concept I would think. I really have no idea what kind of issues you might run into - I would maybe even try this on the duplicate project first.