You can install Mambo on your account via the automatic script installation system - Softaculous. Here is the way of installing Mambo from Softaculous:
cPanel --> Softaculous --> Portals/CMS --> Mambo --> Install
You can also request the script to be installed on your account by SiteGround Technical Support Team. They would gladly assist you with the installation of any script/application that is compatible with your hosting account.
Log in to your Customer Area --> Support tab --> Open a Support Ticket -> Script Installation
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