Change MS Office product key by Registry file

Step:
1) Run -> cmd -> regedit
2) HKEY_LOCAL_MACHINE -> Software -> Microsoft -> Office

3) Select the office version that installed in your machine
a. 11.0 – MS office 2003
b. 12.0 – MS office 2007
c. 14.0 – MS office 2010

Then go to Registration folder, go in the child folder

4) Just go ahead delete DigitalProductID and ProductID
5) Next, open MS office to re-enter the product key.