2) Download the new release of WordPress
(you need to download a release 1-2 versions older than yours; for example, if you want to update your WordPress 1.5, first you put 2, version 2.1 can be skipped, put 2.2, 2.3 skipped, put 2.5, etc. – i.e. to reduce the time we jump through one version).
4) Delete all files except wp-config.php and load a new version of WordPress
(Attention, if you are a pluginomaniac or in you have a lot of pictures, it makes sense to save folders with pictures, plugins, etc.)
5) Run wp-admin/upgrade.php , update the database
6) Enjoy the new version of WordPress. Repeat n-times, until we upgrade to version 2.7, reaching it, you can use auto-update.
Leave any questions and comments in the comments, I will not leave unanswered.