Upgrading an existing Drupal site
1. Make a backup of your Drupal instance.
2. Download the latest release of your current Drupal version.
3. Extract the [tar ball or zip] Drupal package.
4. Set your site on maintenance mode
5. Delete all the files & folders inside your original Drupal instance except for /sites folder and any custom files you added elsewhere.
6. Copy all the folders and files except /sites from inside the extracted Drupal package [tar ball or zip package] into your original Drupal instance.
7. If the update release includes changes to settings.php replace old settings.php in …/sites/default/ with the new one, and edit site-specific entries (eg database name, user, and password)
8. If you modified files such as .htaccess or robots.txt re-apply those changes to the new files.
9. Login to your site as administrator or as user no 1 ==> http://www.site.com/drupal717/?q=user
10. Run update.php by navigating to http://…yourdrupalsitename/update.php
11. Follow the process to update your Drupal instance
12. Disable maintenance mode