But if you use Drupal 5.xx and want to upgrade to Drupal 6.xx this is the tutorial:
1. Backup your database and Drupal directory. So if you get fail when upgrade, you just need restore the backup folder and database
2. Log on as the user with user ID 1
3. Place the site in "Off-line" mode, to let the database updates run without interruption and avoid displaying errors to end users of the site. You can do that from http://www.example.com/?q=admin/settings/site-maintenance (replace www.example.com with your installation's domain name and path).
4. If using a custom or contributed theme, switch to a core theme, such as Garland or Bluemarine.
5. Disable all custom and contributed modules. Remember modules and theme for drupal 5.xx are not compatible with drupal 6.xx
6. Remove all old files and directories from the Drupal 5.xx installation directory.
7. Unpack the new files and directories into the Drupal 6.xx installation directory.
8. Copy your backed up "files" and "sites" directories to the 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 taken in step.
9. Make sure that your new configuration file is correct.
10. Run http://www.example.com/update.php (replace www.example.com with your Drupal installation's domain name and path) from your favorite browser.
Note: if you are unable to access update.php (for example can't login with user ID 1)do the following:
- Open your settings.php with a text editor.
- Change $update_free_access = FALSE; to $update_free_access = TRUE;
- Once update.php is done, you must change the settings.php file back to its original form with $update_free_access = FALSE;
11. If you can run update.php then follow the instruction. If success you will get information about drupal database update.
12. Ensure that the versions of all custom and contributed modules and themes match the Drupal 6.xx.
13. Re-enable custom and contributed modules and themes then re-run update.php to update custom and contributed database tables.
14. Finally, return your site to "Online" mode so your visitors may resume browsing. You can do that from http://www.example.com/?q=admin/settings/site-maintenance (replace www.example.com with your installation's domain name and path).
Have a nice try!