Here is the procedure to upgrade your WordPress Blog to the Latest Available Version at WordPress.Com.
1. Backup your database.
2. Backup all WordPress files in your WordPress directory including .htaccess file.
3. Verify your backup. It is very important to verify that your backup is usuable.
4. De-activate all installed Plugins.
5. Download upgraded wordpress package and extract it.
7. Delete the old WordPress files from the site but do not delete:
* wp-config.php file.
* wp-content folder; Exception: the wp-content/cache and the wp-content/plugins/widgets folders should be deleted.
* wp-images folder.
* wp-includes/languages/ folder–if you are using a language file do not delete that folder.
* .htaccess file–if you have added custom rules to your .htaccess, do not delete it.
* robots.txt file–if your blog lives in the root of your site (ie. the blog is the site) and you have created such a file, do not delete it.
8. Upload the new extracted files to the appropriate WordPress folder on your site.
9. Run the WordPress upgrade program and follow the instructions on the screen.
10. Install updated Plugins and Themes.
11. Re-activate Plugins.