we have purchased lenovo laptop which is already having windows 8.1 single licence.so we have purchased up gradation pack and the we have used the key and the laptop operating system has been converted to windows 8.1 professional with media centre but now the laptops are having some problem so we are going to send back the laptop to lenovo and replaced the same to another model of lenovo with same windows 8.1 single licence.and now i want to use the previous key (the upgradation pack) for the new laptop .please suggest me how to do the same .

Hello siba11111,

About the license issue, it is recommended to contact the local support or the Phone support.

For more information, please take a look at the following KB.
http://support.microsoft.com/kb/950929

Best regards,
Fangzhou CHEN