Simply follow below listed steps:
- Login to your Magento admin panel, e.g. www.yourwebsite.com/index.php/admin123.
- Hover over "System" and select "Configuration". In the "Configuration General" section area, select "Web".
- In the "Configuration General" section area, select "Web".
Changes should take effect instantly – Go to your website and open an image in a new window, the URL will show that content is now being served from the CDN. Alternatively, check your code by right-clicking and selecting "View Page Source" to see assets coming from the CDN.