Back in December 2007 I wrote a post explaining a method to upgrade your WordPress install by simply overwriting the changed files instead of reuploading everything. Back then I was assuming that the “new version available” post will always tell you what files are changed so it’s easy for you to know what to upload.
However, today 2.3.3 is out and the announcement does not mention anything about changed files. Darn.
Trac Browsing to the Rescue
So, I decided to look around WordPress’s Trac. Now, I don’t know much about Trac, so I’ll let Wikipedia explain:
Trac is an open source, web-based project management and bug-tracking tool[...] (Source)
Okay. So, in essence, this is the place where you go to find the WordPress source code in various versions, with notes on modifications and whatnot, from the earliest to the most updated. So it’s the right place to go.
And the nice thing is that it allows you to compare the difference between versions. Exactly what we needed.
First, go to the tags directory of the source. There you can see a list of every WordPress version, from 1.5 to 2.3.3 and everything in between. Choose the most updated version. In our case, 2.3.3.
If you do it right, this page will be opened. At the bottom of the page there’s the View Changes… button. Exactly what we need. Click it.
You will see a form like below:

Except that in your case the input field might still be empty. Well, punch in the numbers the way I did: in the From field it’s “tags/x.x.x“, x.x.x is for the previous version, while in the To field it’s “tags/y.y.y” for the current version. Click View Changes. You don’t have to worry about the numbers on the two Revision input boxes.
And now you’ll see the list of files changed from previous version:

Those are the one you should upload and upgrade. Refer to the old tutorial for more detailed steps.
Now, if you’d excuse me, I have some upgrading to do.