Win 10: cannot update from build 10586 to latest version 14393?

Try updating manually using an Installation media(don't use the upgrade assistant, instead use Media creation tool)

See this article for a detailed guide:

Here is how to update to Windows 10 Anniversary update manually if you are having troubles with Windows update

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Manual steps:

Download Media Creation Tool:

http://www.microsoft.com/en-us/software-download/windows10

Select upgrade this PC:
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Or if you wish to save an ISO for future purposes like Re-Installation download an ISO(Select create Installation media)

 How to download an ISO using Media creation Tool:

http://www.tenforums.com/tutorials/9230-windows-10-iso-download.html

When the download finishes, double click the ISO file and run setup.exe in the new window that opens. Here are the detailed steps

:How to do a repair Install using a windows 10 ISO 

Another detailed article:

http://www.tenforums.com/tutorials/16397-repair-install-windows-10-place-upgrade.html

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