Installing Softaculous Note: Before starting the installation make sure ionCube Loaders are enabled. For that go to WHM and click on Tweak Settings. Please make sure that the Ioncube loader is selected for the backend copy of PHP.

Now SSH to your server and enter following commands:

cd /usr/local/cpanel/whostmgr/docroot/cgi 
wget -N http://www.softaculous.com/ins/addon_softaculous.php
chmod 755 addon_softaculous.php

Now go to :

WHM > Plugins (Add-Ons on older versions than 11) > Softaculous - Instant Installs
The following webpage will open if the installation was successful: