Drupal Update Tutorial
How to update Drupal to a newer version
This is a tutorial about updating one Drupal release to a newer one within the same version; for example, from Drupal 6.19 to 6.26, or from Drupal 7.10 to 7.14.
Before you begin the update make sure you have a recent backup of the database used by your Drupal and of the Drupal files on your hosting account. For more details on how to do that check out the tutorial on backing up your site.
Drupal informs you automatically if there's a new update. You can check that from the admin panel of your Drupal. In both Drupal 6 and Drupal 7 you can go to admin>Reports>Status report to check whether your Drupal is up to date.
Before you start the update process put your site in maintenance mode. You can do this from the admin panel of your Drupal. To do this in Drupal 6, go to Site maintenance, mark the button labeled Off-line and click on Save configuration. In Drupal 7 go to Configuration tab>Maintenance mode, mark the checkbox labeled Put site into maintenance mode and click on the Save configuration button.
You need to download the last stable release for the Drupal version that you use. You can do that from the official Drupal site. After you download the archive to your local computer unzip it. The unzipped archive should contain a folder labeled with the number of the release (e.g. drupal-6.26, drupal-7.14, etc.). Inside that folder are all the files and directories (e.g. includes, modules, scripts, etc.) that you need to upload to the root Drupal directory on your Drupal hosting account. For example, if your Drupal is installed directly in the public_html directory on your hosting account, you need to upload the files and folders that are inside the unzipped Drupal directory on your local computer to the public_html directory on your hosting account overwriting the old files (the ones that are on your account). You can do that with an FTP client (e.g. FileZilla).
Once the files on your account are updated, you have to update the MySQL database used by your Drupal. You can do that by opening with your internet browser the URL address of the update.php file that's inside the root Drupal directory on your hosting account. For example, if your Drupal site is accessible at yourdomain.com, you need to open with your browser yourdomain.com/update.php and just follow the instructions.
After that make sure that everything on your site works correctly and disable the maintenance mode.
In case you had put some additional directives in the old .htaccess file, you can use the copy from your backup and upload it back to the root Drupal directory on your account overwriting the new file. Alternatively, when you upload the files from the new Drupal release just don't upload the .htaccess file. The same is true for the robots.txt file. Although it's not recommended to modify the code of core files, if you do it, you should keep a list of all the modifications so that you can perform them again after an update.