Here is an easy method of deleting outdated WordPress; this is important for keeping your WordPress installation secure from the attacks of hackers. Whenever you upgrade WordPress core; some files which are no longer of any use sets for automatic removal but on some occasions when PHP has no permissions of deleting these files then in that case they exists on your server and this increases the risk of hacking. But now using Old Core Files plugin you can easily get alerts to remove old files before hackers attempt to exploit them for attacks.
Install and activate Old Core Files plugin, after activation visit your admin area Dashboard -> Tools -> Old Core Files page where this plugin lists all those old files which are not needed by your newer version of WordPress.
Other than this it is recommended for all WordPress users to remove unused WP Themes, Plugins and other deprecated code files as hackers may attempt to exploit them for attacks.