How to Change boot device priority or access BIOS in Sony VAIO Laptops?

Few days back one of my friend bought Sony VIAO E-series E15123 Laptop with Windows8. He was not comfortable with windows8 so he decided to change it to Windows7. We have tried complete day but unable to find out how to access BIOS settings to change boot device priority to boot with Windows7 bootable CD. We have tried pressing F1, F3, Delete and many other keys during start up but none of the solutions works. Then suddenly a trick works.

Trick: Just shutdown your Laptop and press assist key. It will automatically power on your laptop and shows you BIOS screen. Hope it will help.