In newer SONY laptops with UEFI firmware, you won't be bale to access BIOS by pressing F2. You can try the below steps instead.
1. Power off the laptop.
2. Instead of pressing the "Power Button" to turn on, press the "Assist" button.
System will be powered on and a menu will be displayed. From there press "F2" to enter BIOS.
3. To install "Windows 7" , you need to disable "SecureBoot" , enable "Legacy" mode and clean the current GPT partitions using DISKPART. However do this only if SONY provides @1 for your model. If SONY is not officially listing any Win7 drivers, you will have a hard time hunting down the drivers. Also you will loose special key functions like adjusting brightness etc.