As we all know, upgrading Windows when it is booted from a USB drive or a VHD/VHDX disk is not supported, this is a limitation of Microsoft. The main function of Windows To Go Upgrader is to remove this limitation. Here you can find out how to upgrade Windows To Go from lower Windows version to higher Windows version.
Check: Check whether a Windows To Go drive can be upgraded?
Upgrade: Upgrade a Windows To Go device.
Tips: The upgrade feature is only available in the full paid version of Windows To Go Upgrader, so you'd better use the check feature to confirm that your device can be upgraded before you make a purchase.