How to Change Windows 7 Product Key

I installed windows 7 ultimate operating system on my desktop. I do not have a product key while installing operating system to make my windows genuine. After installation of windows 7 operating system I activated windows with windows 7 loader. Now I got a windows 7 product key from friend or from internet resources. This time I thought how to insert genuine key, usually there is no option to insert key.
Here is a solution to insert new windows 7 product key to make windows genuine. Try below product key to make windows genuine.

Windows 7 Ultimate Genuine key: 2Y4WT-DHTBF-Q6MMK-KYK6X-VKM6G