For some reason, although you updated the latest theme, but the Visual Composer or Revolution Slider still didn’t work or they are not the latest version. So please do the following these steps :
1. Please ensure you downloaded the latest and UPDATED theme.
2. Access your FTP ( via FileZilla or something else ) or cPanel
3. Go to your directory => wp-content => plugins , find and DELETE js_composer folder.
4. Go back your WordPress Admin.
5. You will see the requirement notice. Click Begin installing plugin.
6. You’re done.
What is your FTP ? Please read here : https://www.siteground.com/tutorials/ftp/ftp_client.htm
Download FileZilla : https://filezilla-project.org/download.php?type=server