Upgrading from 1.7.2 to 2.0.0
Before performing an update you should take your site offline by replacing the index.php file with a static one.
Step 1: Update your CodeIgniter files
Replace all files and directories in your "system" folder except your application folder.
Note: If you have any custom developed files in these folders please make copies of them first.
Step 2: Adjust get_dir_file_info() where necessary
Version 2.0.0 brings a non-backwards compatible change to get_dir_file_info() in the File Helper. Non-backwards compatible changes are extremely rare in CodeIgniter, but this one we feel was warranted due to how easy it was to create serious server performance issues. If you need recursiveness where you are using this helper function, change such instances, setting the second parameter, $top_level_only to FALSE:
get_dir_file_info('/path/to/directory', FALSE);
Step 3: Convert your Plugins to Helpers
2.0.0 gets rid of the "Plugin" system as their functionality was identical to Helpers, but non-extensible. You will need to rename your plugin files from filename_pi.php to filename_helper.php, move them to your helpers folder, and change all instances of:
$this->load->plugin('foo');
to
$this->load->helper('foo');
Step 3: Update your user guide
Please replace your local copy of the user guide with the new version, including the image files.