This is a VC's bug. Basically, since we handle these updates you should not see this message. We have already informed the VC's team about this and they will provide a fix in the next release. Then you will need to remove and reinstall the new version as the auto update will not work because of this bug. So:
- Deactivate the Visual Composer
- Make the update while it is deactivated
- Activate again the VC and you will get the new version which is included in the theme
Notice that there is nothing to worry about this process, you are not going to lose your data :)
Important: There is no need to purchase a licence for the Visual Composer (for any of our themes) as it is included in our themes. Read this article.