Hi,
I’m part way through the course and have already installed Kali, now that there is an upgarde available do I need to do a fresh install or can I update the one on my VM?
Have you installed Veil?
Cause the only way to upgrade custom kali is to install a new machine. Also you can save all the important files in you host machine and then transfere them to the new custom kali, you can use Shared Folders settings in VirtualBox for this.