Windows will automatically choose the version of 10 to install according to your serial key in BIOS or already installed Windows OS. You can force it to let you choose which version of Windows 10 you want to install by creating one file on your installation DVD / USB drive.
Create a file called ei.cfg in the sources directory on your installation media, open it in any text editor and paste this:
[Channel] Retail
Restart the installation process and you will once again be able to select the version of Windows 10 that you wish to install.
