First of all you need delete an old version of Visual Composer on your website.
1. Log in to your admin panel and go to: Plugins > Installed plugins > WPBakery Visual Composer > Deactivate > Delete
2. Make sure if you have latest version of theme purchased on themeforest.
3. In your WordPress Dashboard > Appearance > Install plugins
If you don't see any changes and you still have old plugin version it's possible to extract plugin from theme folder
Don't forget to check changelog and theme description what plugin version included with theme package.