I had problems this morning upgrading to Windows 10 and kept receiving error code 80240020, the below fix has worked for me!
1. Go to C:\Windows\SoftwareDistribution\Download and delete all files in the Download folder – Not the folder itself!
2. Open Command Prompt as an Administrator and type wuauclt.exe /updatenow
3. Open up the Windows Update screen and you should now see Windows 10 Update downloading 🙂 and no more error code 80240020!
If you want to do a fresh install or just want the media for a reinstall at a later date you can get the Microsoft download tool here to create your own installation media using either a USB flash drive or a DVD.