Powershell 3.0 upgrade to 4.0 on win8 PC

Hi ,

My PC is Windows 8 , and was actived by KMS server, I can't upgrade to windows 8.1. 

And windows 8 powershell version is 3.0, I want to upgrade to 4.0. However, After I download powershell 4.0 from below link: http://www.microsoft.com/en-us/download/details.aspx?id=40855 ,I double click the software and pop out an error:

Windows Update Standalone Installer ,

Installer encountered an error: 0x80096002 

The certificate for the signer of the message is invalid or not found .

I checked the link:http://www.microsoft.com/en-us/download/details.aspx?id=40855 and found the fix only support windows 7 SP1 and windows server 2012, doesn't support windows 8.

But I can't upgrade my OS from windows 8 to 8.1, What should I do then?