Upgrade Codeigniter Project to Latest Version

I have one codeigniter app which is having version 2 or something. I need to upgrade the app with the current Codeigniter latest version without any errors.

Initially we have published this app on Codecanyon. Currently due to some errors it got rejected on it. We need to upgrade and submit it again to codecanyon.

So the 2 tasks are :
1) upgrade the latest codeigniter version
2) refactoring it without any bugs (as per codeigniter standards)

Interested connect me with your codeigniter experience details.

*Codecanyon Standards as follow*
1. All JavaScript should be written with “use strict” mode on; For example, you can do this with jQuery:
(function($){
“use strict”;
//Code here
})(jQuery);
2. Use on(); rather than .click(), .bind(), .hover(), .submit(), etc.
3. Data must be correctly escaped and sanitized. Look at your $_POST and $_GET data.
4. No inline CSS. All CSS must be separated into an external stylesheet.
5. No inline JavaScript. All JavaScript must be separated into an external file.
6. You’re bundling old versions of libraries. Please update all your libraries to their latest version.
7. Remove all commented/unused code from all files.