In order to remove the operating system from your computer, you need to format the partition containing Windows 7, or delete it entirely. It is recommended to back up your programs, files and settings because if you format or delete the partition, you will lose all your data. After that, go to Start > Control Panel > System and Security > Administrative Tools and open Computer Management using Administrator rights. Select Disk Management below Storage, right-click the Windows 7 drive, select Delete or Format and follow the provided instructions. For further information, you can check the Microsoft Support page.