Upgrading Drupal 8 to a newer version from the command line using Drush?
To do it via the command line you can simply run the command drush up drupal

To do it manually, it's a bit more tedious as you need to be really careful about what you want to keep, templates.. modules... themes. Basically you need to replace all core files at the root level and note that the files that reside at the root level e.g. .htaccess.. robots.txt need to be compared and merged with the latest.

I hope this helps.