Here is what is from the documentation:
Upload all files and directories from the unzipped UBB.threads™ directory to the UBB.threads™ installation directory, except for the includes, styles, and cache_builders/custom directories. You will want to upload all of the .php files within the cache_builders directory, just make sure not to upload the custom directory or files within it.
Then you would run the upgrade.php file.
At this point since there were not any alter tables. You probably may get away with just uploading the files.
It may seem okay now but the next upgrade may be a issue since the version number is in just about every file.
