Step 1: Download and install plugin
Go to the CDN for Joomla! website to download the CDN plugin. There is a free version as well as a paid version. You can select one of them based on your requirements. For MetaCDN to work, the free version is sufficient.
Login into your Joomla Administration Portal, and click into Extension Manager at the top menu.
In the Upload Package File section, select the downloaded plugin .zip file (no need to extract it) and click upload & install.
Step 2: Config plugin
Click into Plug-in Manager at the same Extensions top menu, search for CDN, and you will find the plugin named System - CDN for Joomla!
Clicking on the name will direct you to the edit settings page of the plugin. At the right panel, put your site's MetaCDN Accelerated URL (***.metacdn.sa.com) into the field of CDN Domain. Click on Save and now you are all done. Congratulations, you can enjoy your accelerated Joomla powered site now!