Revert back to Windows 8, during Windows 8pro installation

Hi, I need your help pls! My uncle purchased a brand new Sony Laptop Vaio with Windows 8. He clicked the button to update them to Windows 8 pro (he said this button was when Windows 8 logged on for the first time). After downloading (normal procedure) Windows 8 pro, and during Installation, he was asked to enter his Windows 8 pro key. He doesn't have any, he thought he would be able to do...