I can update Drupal 7 websites core with following instruction from "How to update Drupal core".
- Make a backup of your Drupal instance (database). (For ex: with MySQL)
- Download the latest release of your current Drupal version.
- Extract the [tar ball or zip] Drupal package.
- Set your site on maintenance mode (For ex: How on D7)
- Delete all the files & folders inside your original Drupal instance except for /sites and its sub-folders. This assumes that all of your custom work - including themes - is in the recommended spot - the /sites folder tree. If you have made custom changes elsewhere you will need to either preserve them or plan to replace them later.
- Copy all the folders and files except /sites from inside the extracted Drupal package [tar ball or zip package] into your original Drupal instance location.
- Some updates do not include changes to setting.php and some do. See There is a way - Comment below for more on this. If the update release includes changes to settings.php you will need to replace your old settings.php in .../sites/default/ with the new one, and then edit the site-specific entries (eg database name, user, and password) in the setting file.
- If you have modified files such as .htaccess or robots.txt re-apply those changes to the new files.
- If you have a favicon.ico file that was deleted replace it too
- Login to your site as administrator or as user no 1
- Run update.php by navigating to http://...yourdrupalsitename/update.php and follow the process to update your Drupal instance
- Disable maintenance mode
I want to know the instruction for updating Drupal 8 core (e.g. from 8.0.0 to 8.0.2). How do I do it?