You need to update the VC plugin files – js_composer and templatera)
You can find the plugins zip file in frameworks/plugins folder.
If you are using ftp method then you need to unzip the js_composer.zip and templatera.zip folder and add the js_composer and templatera folder to wp-content/plugins folder(replace with the older files) .You can check the plugins folder structure in wp-content/plugins folder.
Or You can do with wp-dashboard .
Just delete the older version and add the new one through plugins > add new > import the plugin files which is in the frameworks/plugins folder .