Through the Power Options
Instead of going all the way into the Settings screens, there is a faster way to access the boot options menu. Press Windows key + I (capital “i”) to access the sidebar menu and press the Power button. Press
Shift as you select the Restart option. The Continue, Troubleshoot, and Turn off your PC options display on the blue boot options menu, just as they do using the primary method.

This method also allows you to access the boot options menu without logging into Windows. On the login screen, press the Power button in the lower, right corner of the screen and press Shift as you select Restart.
http://www.howtogeek.com/126016/three-ways-to-access-the-windows-8-boot-options-menu/
or
http://www.makeuseof.com/tag/how-to-access-the-bios-on-a-windows-8-computer/