The standard process of updating is as follows:
- Take backups of all files and database
- Put site in Maintenance Mode (under Configuration / Development)
- Delete all files except the Sites folder and any files such as ".htaccess" and "robots.txt" that have been customized. (This assumes any contributed modules, custom themes etc. That you use are in the sites directory)
- Upload the new files except the sites directory or the .htaccess or .robots.txt files.
- If changes have been made to robots.txt or .htaccess in the new version ensure these are incorporated into your version. The release notes should tell you whether this is required.
- Run Update.php by visiting yourdomain.com/update.php
- While Update.php runs if you got any errors like below use the Module missing message fixer to overcome these errors.(For 7.5x versions only)
The following module is missing from the file system: MODULE NAME. In order to fix this, put the module back in its original location. For more information, see the documentation page.
User warning: The following module is missing from the file system: MODULE NAME. In order to fix this, put the module back in its original location. For more information, see the the documentation page. in _drupal_trigger_error_with_delayed_logging()
- Switch off maintenance mode by reversing step 2
- Take some time to test the site is functioning as expected.
More in-depth information on updating and upgrading can be found at http://drupal.org/upgrade