DietPi VirtualBox more than 8GB

I am trying to enlarge the DietPi VB to 16GB, but it is not happening. I have looked at different online documentation on how to do it, but I seem to not be able to.

Windows 8.1, VirtualBox 5.2.26, DietPi_VirtualBox-x86_64-Stretch

What am I missing. I need at least 16GB, if not 64GB to be on the safe side. All files after processing will be moved out of the VB onto the NAS that is available to the VB.

Thanks in advance!