How to upgrade Drupal 6.15 to 6.19 ?

Updated patch files to Drupal 6.18/6.19

Standard procedure to upgrade Drupal:

1. Download the latest release/patch from drupal.org and follow the included UPGRADE.txt.
   **However,for administrators using the UNIX shell it may be easier using the attached patch files below instead of downloading and installing the newest complete Drupal release.
   
   
2. Download the related patch files from here:
   http://fuerstnet.de/en/drupal-upgrade-easier
   
   
3. Follow UPGRADING.txt up to '5'.
   Let's begin!
   
   1. Back up your Drupal database and site root directory. Be especially sure to back up your "sites" directory which contains your configuration file, added modules and themes, and your site's uploaded files. If other files have modifications, such as .htaccess or robots.txt, back those up as well.
   
   Note: for a single site setup, the configuration file is the "settings.php" file located at sites/default/settings.php. The default.settings.php file contains a clean copy for restoration purposes, if required.
   
   For multisite configurations, the configuration file is located in a
   structure like the following:
   
   sites/default/settings.php
   sites/example.com/settings.php
   sites/sub.example.com/settings.php
   sites/sub.example.com.path/settings.php
   
   More information on multisite configuration is located in INSTALL.txt.
   
   2. If possible, log on as the user with user ID 1, which is the first account created and the main administrator account. User ID 1 will be able to automatically access update.php in step #10. There are special instructions in step #10 if you are unable to log on as user ID 1. Do not close your browser until the final step is complete.
   
   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. This option is at 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.
   
   
4. Remove all of the old files and directories from the Drupal installation directory." Go on using this commands:

   • cd DRUPAL-ROOT
   • Patch: patch -p1 <>
* Be warned: this may break your Drupal installation , so make sure to have a backup at hand.


5. Proceed with UPGRADING.txt from '8'. Verify the new configuration file to make sure it has the latest and correct information.
   
   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 #1.
   
   9. Verify the new configuration file to make sure it has correct information.
   
   10. Run update.php by visiting http://www.example.com/update.php (replace www.example.com with your Drupal installation's domain name and path). This step will update the core database tables to the new Drupal installation.
   
   Note: if you are unable to access update.php do the following:
   
   - Open your settings.php with a text editor.
   
   - There is a line that says $update_free_access = FALSE;
   Change it 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. Ensure that the versions of all custom and contributed modules match the new Drupal version to which you have updated. For a major update, such as from 5.x to 6.x, modules from previous versions will not be compatible and updated versions will be required.
   
   - For contributed modules, check http://drupal.org/project/modules for the version of a module matching your version of Drupal.
   
   - For custom modules, review http://drupal.org/update/modules to ensure that a custom module is compatible with the current version.
   
   12. Re-enable custom and contributed modules and re-run update.php to update custom and contributed database tables.
   
   13. Return the site to its original theme (if you switched to a core theme like Garland or Bluemarine in step #4). If your site uses a custom or contributed theme, make sure it is compatible with your version of Drupal.
   
   - For contributed themes, check http://drupal.org/project/themes for the version of a theme matching your version of Drupal.
   
   - For custom themes, review http://drupal.org/update/theme to ensure that a custom theme is compatible with the current version.
   
   14. Finally, return your site to "Online" mode so your visitors may resume browsing. As in step #3, this option is available in your administration screens at http://www.example.com/?q=admin/settings/site-maintenance (replace www.example.com with your installation's domain name and path).
   
   **Warning

   If you get errors like Reversed (or previously applied) patch detected or 1 out of 2 hunks FAILED while running the patch dry run (second command above) immediately interrupt patching and upgrade following the steps explained in UPGRADING.txt.

Reference Source:
http://fuerstnet.de/en/drupal-upgrade-easier

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