Can the Win8 key activate the Win8.1 system?

A friend bought the key of the Win8 system the year before, and later rose to 8.1, and updated the update. Now he wants to reinstall the system. I don't know if I can download the Win8.1 image and use the Win8 key to activate it. After all, if it has to be slowly upgraded from Win8, it is too much trouble.
First of all, the serial number of win8 can not be directly used for win8.1 installation, it will prompt the serial number is invalid. But win8 serial number can activate win8.1.
can do this:
1. Download the latest win8.1 system image from MSDN, write the ISO file image to U disk or DVD disc, and make installation media.
2. Find an installation key for use with win8.1 (you can use Baidu) for installation. Note that this key cannot be activated.
3. After the system is installed, open the Control Panel > System and Security system, click “ get more features of the new version of windows & rdquo; fill in the win8 serial number, used to activate win8.1. You used to be the standard version after the standard version of the key is activated, and the professional version is activated after the key is activated.
Now everyone understands? The genuine key of Win8 system can activate Win8.1, including the latest Windows 8.1 with Update. So, buy a genuine key, and upgrade to the latest operating system for a period of time is no problem.