Sage is a project/base theme that can be used to build ones own theme.
The theme is separate from the WordPress site and its plugins.
However when you are also using roots.io Bedrock then you manage the WordPress core, plugins and possibly themes using composer
so you mean that, since I am using roots as well, it might be enough to run a composer update in the root folder to have it updated, possibly just updating version code in the composer.json?