Can you pls update theme to latest version – (4.1) , currently you are using very old version theme (3.2). You can download latest version theme from your themeforest account > downloads tab .
BTW we have already bundled VC and rev slider plugin files with theme which have extended licence .
If you want direct support from plugin authors then only there is a need of purchasing separate licence .
You need to update the VC plugin files – js_composer and templatera)
You can find the plugins zip file in frameworks/plugins folder.
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 .