when you install windows it makes itself your default boot option. you should be able to press a button (mine is f12) during boot up in order to bring up the boot menu or BIOS screen.
If you're not able to find the BIOS or boot menu, it might be because Windows doesn't ever do a full shutdown and instead just puts itself to sleep so that when you press power Windows just wakes up.
If this happens, I recommend shutting down windows, then holding onto the power button which will cause Windows to wake up, but keep holding onto the power button until your power is completely killed (15-2