Once the CDN-resource is created in the Client Area, you can setup your WordPress to use CDN easily following these steps:

1. Login to WordPress control panel
2. Install W3 Total Cache plugin and activate it
3. Open plugin settings
4. Go to General Settings -> CDN Delivery Network -> Choose Enable and choose CDN Type as Mirror
5. Save changes
6. From the left menu go to CDN
7. Fill the field ”Replace site’s hostname with” with the CDN URL
8. Save changes
9. Activate changes in the General Settings page

Check from your source code that your page uses CDN. Picture links should be replaced with a CDN url.