If you’re having an issue getting the May 2019 Windows update to install, you may want to try unplugging any external USB drives or SD memory cards connected to your system, including thumb drives.
Some users with these devices connected are getting errors that say Windows 10 can’t be installed.
According to Microsoft if you have a USB drive or SD card attached to the computer it can cause “inappropriate drive reassignment” and prevent proper installation. Just remove the external drive or SD card and restart the installation and everything should go smoothly.
Microsoft says they’ll fix the issue in future updates.