Then to update you only have to do this
*NOTE: Before proceeding backup all files and the database.*
- Upload all new files from a download of the full version, EXCEPT for config.php, the /images and /files folders.
- Go to yoursite.com/forumfolder/install/database_update.php
- Let that run and then delete the install folder.
- You now have a new up to date board containing all your users and posts but without any MODs that you might have had installed.
And make sure you have a 3.0.8 version of your added style as well.