Follow these steps to downgrade to a previous version of Windows or Windows Server software:
Obtain genuine Windows media and a corresponding product key for the version of Windows that is eligible for downgrade.
The media should come from a prior legally licensed version from the OEM or Retail channels.
End users who are licensed separately through Microsoft Volume Licensing (VL) may provide their VL media and key to a system builder to facilitate the downgrade on their own systems.
Insert the downgrade-eligible version of Windows media in the CD drive and follow the installation instructions.
Type the product key.
If the software was previously activated, you will not be able to activate it online. In this case, the appropriate local Activation Support phone number will be displayed. Call the number and explain the circumstances. When it is determined that the end user has an eligible Windows license, the customer service representative will provide a single-use activation code to activate the software. Please note that Microsoft does not provide a full product key in this scenario.
Activate the software.
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