You may experience an error code of 80240020 during the Windows 10 Upgrade process after you've had confirmation that the upgrade is ready to install.
This command should trigger a fresh download of the Windows 10 files into the Softwaredistribution\Downloads directory. Once the files have been successfully downloaded into the directory the upgrade process should start again.
The upgrade process goes through the following stages - Copying files -> Install Features and Drivers -> Configuring settings.
Once complete the system will reboot into Windows 10. You can then delete the temporary folder you saved earlier.