upgrade codeigniter version

My current project has version 1.6.3 of codeigniter framework. Now there is new release of 2.1.0 version of codeigniter. There are many new libraries and helpers included in new version. So I want to upgrade codeigniter to new version to have more functionalities and robustness.

So my questions are:

How to upgrade version of codeigniter framework to latest version?
Is some kind of update provided by codeigniter( like anti-virus)?
If upgraded, will there needs to be change in my current application?

You still have a working web app using CI 1.6.3? That is very, VERY old! Version 2.1.0 is also very old and no longer available to download. Where did you see that version? 

The current version is 4.2.1. The bad news for you is you can't upgrade your old web app to use the latest version. You will need to rewrite everything. 

If you are not in a position to do that, at the very least you should upgrade to 3.1.13. You will have to make changes to your app, but not as much as if you upgrade to 4.

You can find versions 3.x and 4.x here: https://codeigniter.com/download

CodeIgniter 4 tutorials (EN/FR) - https://includebeer.com
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