Almost every month, Wordpress is releasing new security upgrades. If uploading new Wordpress files to an FTP server, deleting the old installation files and running the upgrade setup is too much of a work, then Wordpress Instant Upgrade plug-in is the solution for you.

The InstantUpgrade plugin downloads the latest version of WordPress setup from the WordPress server and unpacks it to your server.
It then deletes all the old WordPress files (except wp-content/ and wp-config.php and language packs) and copies the new files into your WordPress directory.
Lastly, it runs the upgrade script contained in the new WordPress version.

The plug-in requires write permissions to be set on some wp- folders and files. Basically, you need to chmod your WordPress base folder, wp-admin and wp-includes and their subdirectores (except wp-config) to 777. You also need to do the same to the work folder in the plugin directory.

Download the plug-in from here