Visual Composer Security Vulnerability Fix

Hi,

I have purchased a theme on Envato, which contains Visual Composer. The author has stopped responding to any support tickets or comments, and the template has been disabled on Envato.
I just found out about this issue with VC. I bought the item for a client’s website. Current version of VC is 4.5.3. What should I do next & how to update VC to v. 4.7.4?

Thanks for your help!!!