You will not be able to update the Visual Composer Plugin since you need to have license key. We could not give you the license key because it is against the terms and conditions of Codecanyon.
How to update Visual Composer :
1. Update the WPLMS Theme
2. Login via FTP of your server , locate the WP content/plugins/js_composer folder
3. Delete this folder
4. Login to WP Admin and you'll see a notification that visual composer is deactivated.
5. Go to WP Admin -> Appearance -> Install plugins
6. You should see Visual composer, click on install and activate the plugin.
Another way and a much more simpler :
0. Make sure theme is updated to latest version
1. Go to WP Admin -> Plugins -> Visual composer
2. Deactivate the plugin and delete the plugin.
3. Go to WP ADmin -> Appearance -> Install plugins and install and activate the visual composer.
NOTE: Visual composer in WPLMS can only be updated with the theme updates. It may happen that the theme has outdated version of VC if there is a VC update in between theme updates.
Refer Video :