WordPress updates itself manually when a minor release comes up. However, during major updates, WordPress shows a notification whenever an update is available and the user will have the option to continue with the update or postpone it. A user can simply click the button to update it. But there are times when updating from the WordPress admin area is not possible. This is where you’ll need to learn how to update WordPress via FTP.
Before updating via FTP, you’ll need to backup your WordPress installation first. So, in case something goes wrong, you can always get back to your most stable update. If you aren’t able to access the admin area, you can also backup WordPress manually.
Then you’ll need an FTP client installed in your computer. We recommend using FileZilla for FTP because its free and can run on Windows, Mac, and Linux.
Read the rest of the post here: http://www.wpbeginner.com/wp-tutorials/how-to-manually-update-wordpress-using-ftp/