Hi,
The one on display/demo is NOT the one you bought. Your machine is designed to run Windows 8 & 8.1. Windows 8.1 is much, much, much better than Windows 7 and Windows 8. But if you wish to run Windows 7 you can install it and use Windows 7 updates to install drivers. You may ending up missing 2 or 3 drivers, please post back and people on this forum (specially Paul_Tikkanen) will help you.
Regards.