read the versions.txt that comes in the installation package
If you want to read about the changes before you download, see
http://www.mirc.co.uk/whatsnew.txt
hmm. I never knew that was there.
have you seen
http://www.mirc.co.uk/versions.txt ? Has all changes from 28/02/95 - mIRC v2.1a First public release, to the current version. Saves a lot of time when you're trying to remember what happened when, not to mention its entertaining