With the InstantUpgrade plugin, you can easily and safely upgrade your WordPress automatically, with a single click. I found this plugin when visiting to SaifulIslam blog. InstantUpgrade is the wordpress plugin that help us to upgrade wordpress version with just inside the Wordpress control panel. The InstantUpgrade plugin downloads the latest WordPress version from the WordPress server, and unpacks it at your web hosting. It will then deletes all of your old WordPress files (except wp-content/ and wp-config.php) and puts the new files into your WordPress directory. The final step is it runs the database upgrade script. The procedure exactly follow the official guide, only 30 times faster and easier. [1].

(A screenshot from the demo images)

It was well safe to use but however, backups is necessary. Remember to backup your web first. You can refer the Wordpres plugin - InstantUpgrade for more info, download and installation.