When attempting to install Windows 10 it may fail with Error Code 80240020.  You may also notice in Windows Update there is a status of “Failed” new to Upgrade to Windows 10.  This error means that the installation files for Windows 10 have been corrupted.  To resolve this issue you  will need to delete all the files in the Software Distribution Download folder.  Here are the steps:

1. Open Windows Explorer and browse to “C:\Windows\SoftwareDistribution\Download”
   
2. Delete All the files found in the Download folder
3. Open a Command Prompt as an administrator and type in the following:
   wuauclt.exe /updatenow
4. Open Windows Update in the Control Panel and Windows 10 should start downloading again