how to setup code igniter so it's outsid public_html?

[eluser]chobo[/eluser]
Hi, I'm not sure which paths or variables I need to change in order to make code igniter work outside the public_html folder

I want to have a directory structure like this:

Code:

classes
lib
- CodeIgniter_1.5.4
   - code igniter files
public_html
- Images
- JS
- CSS
- index.php

I have no idea how to set this up.