How to change notification sound (WP 8.1) of credit information from operator?

[WPCentral Question]

Hello, I would like to ask, whether it is possible to change sound of notification from my operator like "Your remaining credit is 10?" . The sound "Telekom Message" is irritating for me, I would love to change it, but nowhere in Options I cannot find options to change this particular sound, I can change my ringtones and sound for messages and other apps, but not for this... Thank you for replies