- Backup your entire database first.
- Download Changed Files from here: http://blog.mybb.com/2010/12/15/mybb-1-6-1-release-1-4-14-update/
- Upload the changed files and overwrite to the old files.
- Now run the upgrader using the following link: http://www.yourdomain.com/install/upgrade.php
- Point the old version, and follow the instructions appears on the screen.