I just found this very useful link on the wordpress.org website!!
If you have shell access, you can get a copy of the latest stable build of WordPress in two easy steps. Now how cool is that? =)
1) wget http://wordpress.org/latest.tar.gz
2) tar -xzvf latest.tar.gz
“The WordPress package will extract into a folder called wordpress in the same directory that you downloaded latest.tar.gz.”
To complete the upgrade, you will need to copy the required files (.htaccess, wp-config.php and the wp-content directory) from your old WordPress installation into this new one. Move the old one, rename the wordpress directory to your old name and you are ready for the last and easist step…
http://your-domain/blog/wp-admin/upgrade.php
WordPress really can be upgraded in under 5 minutes!