To access Boot Order in a PC, you need to press some specific keys when the computer stats turning on.
As soon as you turn on the computer, notice at the bottom of your screen, you will see some options, one of them will point to BIOS,
(Eg: F10 BIOS).
Start Tapping as you see that option.
Doing this will take you to a Blue color BIOS Screen (which is stored on CMOS chip).
One of the Tabs at the top will be "BOOT", use the arrow keys on your Keyboard to navigate (mouse wont work in BIOS).
once you are in BOOT option, you will see the option for BOOT PRIORITY or BOOT ORDER.
Just change the order as per your need.