Before you take any steps please back up your files and database. The plugin works only with default CMS pattern. If you manually changed CMS patterns, the plugin might not help you.
Create a CDN Resource.
Download the module for OpenCart.
Install the CDN77 Services module by uploading folders Admin and System to the root path of your website so these files are merged with the existing ones.
Go to the admin panel of your OpenCart store and open the modules list on Extensions -> Modules.
Click on the Install button on the right side to install a module.
After the installation is done, you have to list the modules again and go to the Edit button on the right side of modules list in the CloudCache module row.
Enter your CNAME (cdn.site.ru) that you specified in the G-Core control panel in the Custom Domain/Temporary URL field. Ensure that your CNAME record has been configured in a proper way before using it for integration
Click the checkboxes next to the file types you would like to deliver through the CDN (Images, JS and CSS).
Click on the Save button to save all changes.
Integration has been completed! We highly recommend you to check the HTML code of your web page to ensure that URLs have been rewritten properly from your original ones to CNAME from the control panel.
To do that press F12 or open Developers Tools in your browser, choose the Network tab and refresh the page. All static files should have your CNAME in URLs.
If your site is still not integrated with the CDN after you finish this guide, please make sure compression is disabled in your opencart settings.
There are other plugins for integration with a CDN if you are using CMS Opencart, they are available here.