Read the dev blog.
Backing up your database and files is recommended before ANY upgrade
==== The official method.====
Upgrade just like any other upgrade:
/wp-includes (but NOT your languages folder!!)
all wp-* files at root EXCEPT wp-config.php
(Leave /wp-content and /wp-images alone.)
- upload the replacements for what you have deleted (so don't upload /wp-content or /wp-images)
Use the link in the Dev blog to read the Codex page on upgrading.
There is no need to run upgrade.php after doing this.
====The UNofficial method====
Right now I don't have the changelog, but a list of the changed files is below. If you do it this way, you are on your own as far as support is concerned.
These can be downloaded from here:
Before posting questions, please read all other posts in this thread and also the Codex page. It may well save you time.