quoting a dev:
At present you can set your favorite password only in the yuPlay client application. This app available for Windows only.
You should to go through the steps:
1. Download the yuPlay client installer:
http://yuplay.com/download.php
2. Install and execute the application
3. Log in using your forum login and password
4. Click menu "System" -> "Change password..."
5. Select "I want to use my own password"
6. Type password, its confirmation and press "OK"
Keep in mind that after installation the yuPlay client will be added to Windows autorun. To delete it from autorun, just go to the client's menu "Settings" -> "Program settings...", uncheck "Start with Windows" and press "OK" button.
hope this helps, its done in 5 mins