I tried to use urbackupsrv mount-vhd and to browse an image backup via the browser. This works, really cool!
But how do you unmount it? 
Hi! Still no answer?
Still not enough info, answer will vary according to being mounted under Windows or Linux.
(open script, read how it’s mounted, issue reverse command)
Without that information, the sledge-hammer to crack a nut method works, put simply:
Reboot.
Don’t even need to read how it got mounted or know which OS to figure that method out. It’s kinda brutal though.