The reason you don't see the screen is, most likely, because you're already running Windows 7. There is nothing to upgrade.
To upgrade your Windows installation you must boot into Windows and install from there. If you want a custom installation, you must boot from a Windows installation media.
To perform an upgrade, you can't start, or boot, your computer from the Windows 7 installation media.
So you will only have one valid option in either case.
However, the source linked above shows that there should be the selection screen. But, to my understanding, it will always be an upgrade installation when performed from a booted Windows installation.