Strange code and Visual Composer Installation fails

Since some days I see a strange code on my website which I created with WordPress with a Highend theme. Moreover in the WordPress Dashboard I see a message with asks me to update the Visual Composer.
When I tried to update the Visual Composer I got the message that the installation failed and that I need a higher version.
Then I contacted the WordPress support team and they told me to get in touch witch WP Bakery. I bought the visual composer and thought that this might solve the problem. I tried to install the version I bought but the installation failed as well. The error message says that the destination folder already exist.

Then I contacted the support team of WPBakery and they responded me:

The issue is because your theme originally came with an older version of visual composer. This is an indirect license purchase which do not allow the plugin updating and hence the standalone license is required for updating the plugin. However it is not working because there is already an older version present at your end. You need to first delete it, so you can install the newer version. You can directly delete it from plugins -> all plugins section or via FTP, but I would recommend checking the same with theme author. Because if he has modified any code, then it will be lost upon deleting it and hence some functionality at your end might not work as expected. Upon doing so, you can install the latest version.

Can you please tell me what I have to do to get rid of the code on my website and if I really have to buy the visual composure and if so, how to install it. My website is optimalprice.ch.

Best regards, Christian