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Try Windows update Assistant firstly, this tool can help you upgrade to 2004versio.
If Assistant failed, in-place upgrade by an iso image is also a common upgrade method.
Try to download media creation tool from Microsoft website by click Download tool now button
https://www.microsoft.com/en-us/software-download/windows10
Next, choose ISO file option in Windows 10 setup interface. After iso file download complete, do the following steps:
disable completely the internet on the computer
disable all security software
clean boot the computer
install iso wait for upgrade