Upgrading is simple. Please use the following steps. 

1. Make a backup of your database using phpmyadmin or mysqldump
2. Unzip the new version of Duet
3. Upload the new version to your web server. Make sure to upload to the same exact directory as your previous installation. You want to overwrite the old files. 
4. Once the new files have been uploaded, navigate to your installation in the browser
5. add '/install' to the end of your url. So if you access Duet from http://example.com/duet, you'd access the install at http://example.com/duet/install
6. Run through the install process again and verify that no information has changed. If nothing has changed, simply keep hitting "Next" until the process has completed and the database has been upgraded.
7. Delete the install folder from your server, and log in as usual with your existing credentials.