Re: You can update system with small SSD by using a external drive during update.
in my experience using a USB memory stick as extra storage does not work. You end up with it sat on 0% for hours after the reboot unless you remove the memory stick. But then later it asks you to put it back into the PC and the upgrade fails.
I tried for a whole day to upgrade from 1809 last week and kept getting this exact problem and just gave up in the end. I am going to wipe and install from scratch instead as the whole feature upgrades is just a nightmare.