Upgrade from a version of WordPress to another superior is very easy, so easy that this article will be really short.
Actually since version 2.7 it is not necessary to do this manually, since WordPress includes a system of automatic updates that you will find in Tools »Update and that changed in version 3.0 to Desktop »Updates.
The first thing we must do is download the latest version of WordPress, if possible in Spanish.
We unzip the folder and we only have to copy or overwrite the new files, for the old ones, except the file wp-config.php or some other that we have modified manually.
Finally, we just have to put in the browser:
And click on the button that says: Update database, or something like that. That's it!! It's over!! Donate !!