Updating from Windows 7 to Windows 10 Build 9926

In services.msc, disable and end “Windows Management Instrumentation” (service name “winmgmt”)

Reason: Used to force Windows Update Installer to use another method than WMI to detect RAM (which in my case was 64 MB)

Uninstall virus scanner (in my case avast!)

Reason: Virus scanner blocked Windows Update Installer to write to system partition (even when using virus scanner’s “completely disable” feature)