WordPress 3.9 was released on 16th April 2014.
Update to WordPress 3.9 using the same process as shown for WordPress 3.6
Remember
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.