It turns out the /home directories in my Ubuntu VM were too small to transfer over to a separate partition. I ran “Disk Usage Manager” (I think) and discovered that one of my main directories (/usr or /lib) was using almost all the free space available. It was a good idea to use VBoxManager to boost the space available for the hard drive in the VM. However, GParted does not allow modification of the partition it’s running on.
I realized I had to run a GParted Live CD on the VM. I found the .iso file and left it on the desktop. I had to modify the VM settings to read the .iso file first when booting. Once I figured that out, I was able to run the GParted Live CD. I was still having trouble reordering the partitions of the Ubuntu VMs.
It turns out that the extra space was added at the end of the Linux swap partition, as separate unallocated space. Eventually, a Google search helped me realize that I needed to move the Linux swap space to the far end of the unallocated partition, then extend the “boot” partition over to fill the remaining space. (It’s weird. Why not just one command instead of two separate actions?) I reshuffled the partition space, rebooted and Ubuntu started again with the full 16 GB partitions correctly.
Unfortunately, I’m still having trouble with Ubuntu updates. I can finally run them without running out of free space, but I have a configuration problem where a linux-generic update depends on another file that is not loaded and that file won’t load because it’s not needed. More on that later.