Try updating manually using an Installation media.
For immediate download follow:
Here is how to update to Windows 10 Anniversary update manually if Windows update doesn't find it
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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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