I assume you are wanting to upgrade to cacti 1.1.3? There are a couple of things you will have to do:
1. Get Apache and PHP 7 working successfully together (I recommend testing this on a separate environment and documenting the steps)
2. Download the latest cacti and upgrade
The upgrade process for Cacti is relatively easy. You just need to backup your current cacti, un-tar the new cacti, rename it then head to the web interface to upgrade the database. Simples!
What is your current situation exactly? Have you downloaded Cacti 1.1.3? Do you have PHP 7 and Apache working, or are you not sure?