With WordPress BETA releases you can check new coming features of WordPress and test them locally on your computer or somewhere else. Example: For testing WordPress 3.6 you can download its beta .zip file here, upload them to a hosting or locally on your computer server, configure them just like you do with WordPress stable release installation and check it. Or you can replace WordPress core files on any running WP website and check BETA release, but remember its recommended not to run any BETA release on a production website. This tutorial explains you how you can easily upgrade WordPress to recent BETA releases by installing and activation a simple WordPress plugin.
WordPress Beta Tester lets you to easily upgrade to BETA releases. The plugin provides an easy way to get involved with BETA testing WordPress. After activation it enables you to upgrade your weblog to latest BETA or Release candidate at the click of a button using inbuilt upgrader. By default once enabled the plugin switches your WordPress install onto the point release development track.
To be more adventurous you can select the option to switch to the bleeding edge of development from Dashboard -> Tools -> BETA Testing and then run the WordPress upgrade as usual.
Note: Don’t forget to backup before your start!