What version of CI am I running

Hi all,

I am new to CodeIgniter and I have been handled a legacy system using CI. I am wondering where can I find what CI version the system is using? I opened a few php files and although they all have a version number in them there seem to be several different numbers.

Granted, it seems like I inherited a 1.x version. So I am also wondering if it's worth it to migrate to the latest version (3.0.1)? And what kind of hurdle I should expect?

Thanks for the help