Changing the properties of a Sound Class within´a blueprint!

Hey guys!

I’m trying to manipulate the sounds within my game, through a settings menu.
I’ve come to the part where I’m designing my audio settings menu.
I’ve decided to use Sound Classes (Music, Ambiance, Voice, etc.), and now I wish for the user to be able to change the volume of these Sound Classes, thereby changing the volume of the sounds inheriting this specific sound class.
I can’t figure out how this works, as I can’t find any blueprint node, allowing me to access the Sound Classes.
Note: I’m not working inside the Level blueprint, but inside a UMG widget’s graph

Any help appreciated! Thanks in advance!

https://drive.google.com/file/d/0B4mHdRZLIoRFbkp4ZUpoeS0xRHc/view