This article will show you how to change Grub default boot for any installed operation system inside your computer, be it various Linux or Windows. The steps here known to working very well in my Ubuntu 14.04, while other version or distribution may have similar method.
$ sudo cp /etc/default/grub /etc/default/grub.bak
$ sudo nano /etc/default/grub
After saving above file, then issue this command:
$ sudo update-grub
$ sudo reboot
You can search MenuEntry Label on this file: /boot/grub/grub.cfg