If you already have WordPress 2.7 or 2.7.1 RC1 installed, you’ll receive an update notification that will allow you to upgrade WordPress from within WP-Admin itself. You can upgrade by visiting Tools > Upgrade in WP-Admin. This will upgrade the files and the database as well in one step.
If you’re using 2.6.x or below you will need to manually upgrade.
Unlike earlier, I won’t be providing any upgrade file since, WordPress has made this possible and that is the easiest and recommended method to upgrade your installation.