most people use a pc to copy it from and to sd or usb because that works eazy
and if you want to do it from the pi i use winscp on a pc it’s just drag and drop…
Volumio shares a folder called Internal you can see from any other devices on your network (on Windows you have to enable discover function on network if not already activated). Volumio shares using samba. So, from a file explorer, just drag and drop files you want.