I heard that many people fail for doing that.In case anyone else is having the same problem here's a Solution for Windows 10 update error code: 80240020 that worked for me.
Go to C:\Windows\SoftwareDistribution\Download and delete all files in that Download folder. Do not delete the Download folder though.
Open Command Prompt as admin and type this command
wuauclt.exe/updatenow
Go to windows update and you should see it will begin to download Windows 10
Dont do this. Let it naturally or use the ISO.