WordPress 3.9 was released on 16th April 2014.
Update to WordPress 3.9 using the same process as shown for WordPress 3.6
Update to WordPress 3.6Remember
Before applying any update remember to take a backup and confirm that the backup file will unpack.
See also
- WordPress.org: WordPress "3.9 Smith"
- Perform backups
- You should also update the oik base plugin to version 2.2 or higher.