Follow these steps to change your product key in Windows 7.

Note: If you bought an edition of Windows 7 other than what's installed on your PC—for example, if you purchased Windows 7 Home Premium, and Windows 7 Ultimate is now installed on your PC—you'll need to perform a custom installation to update your product key.

Important: You'll need your new product key to complete the product key update process. For examples of where to find your product key, visit the How To Tell website.

1. Click the Start button , right-click Computer, and then click Properties.

2. Scroll down to the bottom of the window that appears, and then, under Windows activation, click Change product key. If you're prompted for permission to continue the process, click Continue.

3. Follow the instructions to change your product key and activate your copy of Windows 7.

Follow these steps to change your product key in Windows Vista.

Note: If you bought an edition of Windows Vista other than what's installed on your PC—for example, if you purchased Windows Vista Home Premium, and Windows Vista Ultimate is now installed on your PC—you'll need to perform a custom installation to update your product key.

Important: You'll need your new product key to complete the product key update process. For examples of where to find your product key, visit the How To Tell website.

1. Click the Start button , right-click Computer, and then click Properties.

2. Scroll down to the bottom of the window that appears, and then, under Windows activation, click Change product key. If you're prompted for permission to continue the process, click Continue.

3. Follow the instructions to change your product key and activate your copy of Windows Vista.

To change your Windows XP product key, you'll need to use the Windows Product Key Update Tool. Before running the tool, read all instructions to make sure that you understand how the tool works and what information is sent to Microsoft as part of the update process.

Note:‌ Microsoft recommends creating a system restore point before making any operating system changes.

Important: You'll need your 25-digit product key to complete the product key update process. For examples of where to find your product key, visit the How To Tell website.

To update your product key

1. Open the Windows Product Key Update Tool.

2. When prompted to run or save the Windows Product Key Update Tool installer, click Run.

3. Follow the instructions in the installer.

After updating your product key, you will be required to activate Windows XP. If you still have issues after running the tool or with activation, visit the Windows XP Solution Center on the Microsoft Support website for additional assistance.