Drupal Upgrade Process Involves following steps:

• Taking Back up your existing site and database.
• Uploading the latest Drupal files to your server in order to fix security issues and take advantage of many new features
• After the process we need to see whether the contributed modules we rely on have been upgraded or not because the old versions of modules do not run on an upgraded version of Drupal. (e.g 4.7 modules do not work on a Drupal 5.x site
• Unzip the new Drupal files to the server and run the update.php script, which will update your database.