An update is available, should I apply it?
If you’re running an unmodified version of the theme, apply the update to benefit from the latest changes (see the release notes for the theme to see what the changes are). Any configuration changes you’ve made through the theme editor will be retained, as will all of your store content.
If you have a modified theme, it is disconnected from the update feature; updating the base theme won’t affect the modified copy. To benefit from the updates in the latest theme you would need to make another copy of the base theme and re-apply the modifications.