i would like to upgrade project from 1 to last version of ci

long time, i never touch CI. i have used CI to build 2-3 projects. it's very good framework for me. today, i need to update old project that it's made by CI 1.0. i don't know exactly that it's impossible to upgrade to be latest version of CI or not. can you tell me that it's possible to do like that?. thanks in advance

we can't see the code so no one is going to be able to tell you but it should be doable. my suggestions would be 1) get codeigniter 3 running on your server. 2) add the database credentials and confirm it works 3) carefully work through the tutorial in the codeigniter 3 manual. At that point you will be familiar with CI 3 and you won't waste a bunch of time trying to chase down configuration issues.

Then take one controller (and its dependent models and views) from your CI 1 project and integrate it into CI 3.
Thats going to give you a sense of what kind of changes you will need to make. Create a list of search / replace for code changes and update the code with an editor like Sublime that can search/replace across the entire project. Then move one controller at a time into the new project, testing as you go.

the other thing to keep in mind is that in your CI 1 project - apart from the code changes to move up to CI 3 - if this was originally PHP 4 code then there might be changes etc to conform to PHP 5.