OPTION 2 - MANUAL UPDATE:
1. Re download the theme files on ThemeForest (ThemeForest always have the latest version of the theme). So login to your Envato account, then go to Downloads, and download "Install able WordPress file Only" package.
2. Go to Wp-Admin > Appearance > Themes and activate another theme such Twenty Fifteen.
3. Delete the Theme you want to update. (Yeah, you must delete the theme before re-uploading the same theme).
4. Go to WP-Admin > Appearance > Themes > Add New and Upload the Nutritius.ZIP file you've just downloaded from ThemeForest.
5. Activate your theme by clicking the "Activate button".
6. Make sure to reactivate the plugins by going to WP-Admin > Plugins.
7. When the theme update is done, please go to WP-Admin > Appearance > Install Plugin and click "update" for every plugin that requires an update.
8. If for some reason you see some code on your front-end website after the theme update, make sure that all the required plugin are activated by going to WP-Admin > Plugins.
9. If one of your plugins has not been updated (ex: WPBakery Page Builder), go to WP-Admin > Plugins and delete the plugin then go to WP-Admin > Appearance > Install Plugins and reinstall the plugins. Make sure to "activate" it again.