CodeIgniter is a PHP framework for rapid application development. It’s exceptionally fast and it comes in a small footprint. Installing CodeIgniter is fairly straightforward. You just upload the CodeIgniter files and folders to the directory of your choice.
But, for a much more secure installation, you should probably move the application and system folders above your webroot folder, so that nobody has direct access to it. In addition to moving them, you also need to set the full server paths in the main index.php. You will need to edit index.php found in the main CodeIgniter folder.
Change the following entries to:
$system_path - '/full-server-path/system';
$application_folder = '/full-server-path/application';
Save. That should do it.