Noticed that a lot of people are having difficulty in upgrading from drupal 5 to drupal 6 and this post tries to address this process in 15 steps. I tried to put into words what this drupal upgrade tutorial shows in video format - http://www.masteringdrupal.com/screencast/upgrading-to-drupal-6 and then some more.

1. Make a backup of all files and database. If anything goes wrong during upgrade process, than you can restore your Drupal 5.x web site. Must make a copy “Files” and “Site” Folder from the Drupal installation directory. It is highly recommended that you do the upgrade on a local copy or development copy and then move it to production.

2. If your site needs some particular module, ensure that those modules are available from their respective module pages for drupal 6.x because few Drupal 5.x modules are still not available.

3. Upgrade drupal and all installed modules to their latest versions available first in Drupal 5.x. This will eliminate tons of problems with regards to compatibility(schema 1021 and earlier). You can check on available updates for your 5.x drupal install using the Update Status module.

4. Disable all contributed modules and set your Drupal site to default theme such as Garland or Bluemarine. You should update modules and themes after you have completed core Drupal upgrade first.

5. From within, Drupal 5.x administrator panel. Navigate to modules setting page. Disable update_status module and uninstall this module this has been appended to core in drupal 6.

6. Also, from the Drupal 5.x admin panel, navigate to Logs -> Status report. Fix any problems here before upgrading.

7. Login as the first user and set your Drupal site to off-line mode. This can be done as follow. In Drupal admin panel Navigate to : Administrator -> Site Configuration -> Site maintenance -> select site status as off-line -> Save Configuration. You could consider making a backup at this point. This will help you if something small goes wrong during the install and you need to start over. Also it's good to review the minimum drupal 6.x requirements at this point.

Web Server:
Apache 1.3 or Apache 2.x hosted on Unix/Linux or Windows.
IIS5 or IIS6, IIS7 if PHP is configured correctly.
PHP:
Recommended: PHP 5.2 or higher.
Required: PHP version 4.3.5 or higher.
Database Server:
MySQL 4.1 or MySQL 5.0
PostgreSQL 7.4 or higher

8. Delete all drupal files from the Drupal installation directory.

9. Download the latest version of Drupal 6.x from drupal.org. Unpack the files and upload it to the Drupal installation directory.

10. Copy and paste “Files” and “Site” folders from your backup to Drupal installation directory. If other system files such as .htaccess or robots.txt were customized, re-create the modifications in the new versions of the files using the backups.

11. Run update.php by visiting http://www.YOURSITENAME.COM/update.php (replace www.YOURSITENAME.COM with your Drupal installation's domain name and path. ex: http://drupal.org for the official drupal site).

12. Download and replace all non-core modules to their latest version for drupal 6.x

13. Enable your non-core modules and re-run update.php to update custom and contributed database tables.

14. At this point, if you noticed no errors, you may bring back your original theme for your site and enable it.

15. Login to admin panel and set your website status to online mode.

Let us know how your upgrade went and if you had any further issues that may be helpful to others.