Upgrading Codeigniter.php

Hi there, our server is reporting that the Codeigniter script is out of date and is currently a vulnerable file for uploading malicious files. This was confirmed earlier today when a file was uploaded, ran and took our site down for 30 minutes.

Could you advise how I could update Codeigniter please?

https://www.codeigniter.com/user_guide/i...ading.html