This is How to Install and Upgrade to Windows 10 on Your PC. If you wish to keep all your files then click upgrade and not clean installation and key will auto activate. If it doesn't activate online automatically from the integrated BIOS product key, then you must wait for Microsoft to send a new key to your email confirmation you registered or reserved a copy with. You can still use Windows 10 in the mean time. Also remember that if you do a clean installation, you may have to reinstall some drivers (audio, etc) on the computer's manufacturer's website. Make sure you click WINDOWS 10 on the manufactures website when it asks you for which windows edition to install the drivers for. You can also restore back to your previous windows by searching "reset this pc" and clicking "reset this pc" in the search." Then click on "Restore to a previous windows version."