There’s two ways to do this depending on what level of complexity you are OK with.
im doing this from memory, so I may have some menu items wrong – but I can fix that later if you get stuck.
in both cases:
get a USB keyboard and mouse to connect to Beomaster 5. Put the beosound 5 into service mode (move the cursor to Maintenance( I can’t remember exactly the option) then press ><><GO on the beosound 5. Move the wheel to service mode. And then Go. Then you have a windows screen up (on the beosound 5) which you can control with the mouse and keyboard.
Open the Drive E: (it’s the data drive) and choose the BM-SHARE folder then go into Music.
now option 1, you can delete the folders you don’t want here using the mouse and keyboard or option 2 you could set up drive E as a network share (if it isn’t already) and use your computer to mount the drive E: on your own computer and manage the folders from that.
exit by clicking on the exit service mode icon.