Upgrade Windows 7 Home Premium to Professional

1. Right click on Computer -> Properties

2. In System Properties, click on: Get more features with a new edition of Windows 7 to launch Windows Anytime Upgrade wizard.

 

3. Select applicable option below:

4. Click Next to allow Windows Anytime Upgrade to verify the entered key.

5. Accept the "Microsoft Software License Terms"

6. Reboot to complete the upgrade.

(Picture Source: http://www.intowindows.com/how-to-upgrade-windows-7-home-premium-to-professional-or-ultimate-edition/)