Please read the whole thread - many people have added useful information !
This applies ONLY to an upgrade from 1.5 to 1.5.1 - it is not the method to use if upgrading from an earlier version.
It may look complicated - it isn't!
- BACKUP your database
- Download 1.5.1. Unzip it.
- Open the unzipped folder, and DELETE wp-images. (You have no need for these in an upgrade)
- Now open your ftp program and go to your blog directories
- On the server, delete the directories wp-admin and wp-includes. Note: If you have "languages" directory in your wp-includes folder (with .mo files) you may want to save/backup those before deleting the wp-includes directory. Upload the new ones.
- The Classic and Default themes have been changed slightly so if you wish to, you can upload those to your wp-content folder.
- On the server and at blog root, delete the old WordPress files and upload new ones. I recommend you do this one by one if you are not sure. Do not delete wp-config.php.
- Now run "www.example.com/wp-admin/upgrade.php"
(See the post below this)
You don't go near your wp-content folder so your themes and plugins are perfectly safe. this is a very easy upgrade - probably the easiest one yet for WordPress.
Please use a proper ftp client.
Please don't think it's easier to overwrite and not bother deleting files first - you will get errors, you'll post here for help, we'll tell you to do it properly, you will and the errors will go away. Far easier to cut that middle stuff out :)
If you wish, you can delete the following files: