Read the Detailed Upgrade Instructions if you want more intricately carved steps!!!
Upgrading a customized copy of WordPress can be a little tricky. Fear not. This guide will help make quick work of upgrading your jazzed-up WordPress! We watch out for you and will provide pointers to protect yourself against disasters (which other software providers might call "user errors").
Before we start, you need to understand that WordPress is easy to upgrade. Preserving your customizations is the part that makes this a 5-step process instead of 3-step one. We would like you to believe this is a 5-minute process, but the part about backing up your stuff might take a little more than 5 minutes if you are a prolific blogger.
The steps to a healthy upgrade are as follows:
Let us assume your blog has a URI like http://example.com/wordpress/.
Here, the objective is to save the data, and your customizations.
Basically, save the files that you have changed or added since you installed the plain-jane WordPress. Use a FTP tool to download a copy of all the files on the server, in the directory where you installed WordPress, including the .htaccess files if you have been playing with it. Backup at least the .htaccess file, the files used by your current theme (which will be in the /wp-content/ directory), the /wp-images/ directory with your uploaded images and files, any WordPress core files that you modified to use some "hack" directory, and the wp-config.php file which contains your database username, password etc.
Deactivate all the Plugins you use at the Plugin Management Page ( http://example.com/wordpress/wp-admin/plugins.php ). Some Plugins might not work with WordPress 2.0, and that is why you want to deactivate them all. This will ensure that you don't end up with an upgraded-but-broken installation of WordPress after the upgrade process.
Get the latest and greatest WordPress and upload it to the WordPress directory, overwriting all the files that exist there. This will preserve your images and themes. What if something goes wrong, you ask? Well, did we not create a backup of all files in Step 1? You can fall back upon them in the worst case scenario.
Visit your blog's Upgrade Page ( http://example.com/wordpress/wp-admin/upgrade.php ) and follow the trail.
Awaken the monsters, one by one, at the Plugin Management Page ( http://example.com/wordpress/wp-admin/plugins.php ). Check if everything works as expected. There is a list of Plugins that are known to work with WordPress 2.0 here. If some Plugins do not work, accept your fate, nag the plugin author or wait for others to pester the author.
There, that does it.
Something went wrong, you say? No worries. You backed everything up earlier. Restore the files and database tables you backed up, and this time, maybe you should follow the Detailed Upgrade Instructions.