Upgrading and determining current version

You can anywhere in your code use the following, you don't need to find the file itself.

PHP Code:

<?php echo CI_VERSION; ?>

As for where the system folder are (or it have been renamed) you can look for it in your index.php file "$system_path".

After you how found your version, use these upgrade guides. You should read them all, but you can grab the latest version and replace all those files with those instead of going thru them all.
https://codeigniter.com/user_guide/insta...ading.html