The most awaited WordPress version 3.9 "Smith" is released on 16th April 2014 to all. The new version looks promising and can be easily updated from the dashboard in a minute.
To know the new features, click here
To know the change logs, click here
To know how to update WordPress, click here
Important: Don't forget to backup the website and database before upgrading. If you are using any cache plugin, do not forget to empty all the caches after upgrading WordPress successfully.