Some users have reported the occurrence of the 80240020 error when upgrading to Windows 10. This error is due to corrupt installation files on your computer.
To solve this problem, you need to delete some files from your computer and then force the upgrade to Windows 10.
How to fix this error?
Delete the update files
You must first delete all the corrupted files from your computer. As it is impossible to know which file is corrupted, you need to delete all the content of the Update folder. Right-click on Start > Run and type the following path:
Open the Update folder, and delete all the folders and files it contains.
Force the upgrade to Windows 10
Now that the installation files have been deleted, you can force the automatic upgrade to Windows 10. Right-click on Start and open the Command Prompt. Type the below command and then confirm by pressing the Enter key:
Go back to your update manager (Windows Update), and then click Check for updates. Windows 10 should appear in the list of available updates.