Steps to Request a Downgrade Kit

Obtain a copy of the Certificate of Authenticity (COA) and Invoice for the Operating System purchased.
     
For assistance with locating your COA, please refer to the following: http://www.microsoft.com/en-us/howtotell/Software.aspx
         
    Call Lenovo Technical Support to request the Downgrade Kit
     
Support phone numbers may be found at http://support.lenovo.com/us/en/supportphonelist. When calling please make the selections to speak with the appropriate hardware support team.
         
You will be asked to email the Proof of Purchase (a copy of the COA and Invoice) to Lenovo Technical Support. (The email address will be provided when you call in with your request.)
         
        You may also be asked to supply the following information:
            Company name
            Contact person name
            Shipping address
            City, State, Postal code
            Telephone number
            Email address
            Machine type of the server
            Serial number of the server
            Which version do you want to downgrade to?

Lenovo Technical Support will validate the COA and Invoice and place the order to ship the Downgrade Kit to you.

        You may be charged for shipping and handling.
         
        You will receive the Downgrade Kit, which contains the following:
            Downgrade Media (DVD)
            Product Key

Details can be found at this link  which is a sample fot he TS440

https://datacentersupport.lenovo.com/jp/en/products/servers/thinkserver/ts440/solutions/ht101582