You an easily enable CDN in Magento by following these instructions:

1. In Magento control panel, go to Admin > Configuration > Web > Unsecure.
2. Update the following with CDN addresses:
Base Media URL:
Base Javascript URL:
3. Save changes
4. Go to Magento Admin > Configuration > Current Configuration Scope: Main Website > Web > Unsecure > Base Skin URL.
5. Deselect Use Default for the Base Skin URL
6. Update Base Skin URL:
Base Skin URL:
7. Save changes

Check your sites source code that is uses CDN. Picture links should be replaced with CDN URL addresses.