1. Examine /boot/grub/grub.cfg to find out the boot order of your multiboot system or just remember the order of your boot options as they appear during boot.l Count which one is windows (counting is 0-based, i.e. the default boot option is 0, next one is 1, etc).
2. Edit /etc/default/grub. You need to be logged in as root to edit this file or to use sudo, e.g.:
$ sudo emacs /etc/default/grub
3. Look for the GRUB_DEFAULT option, usually it’s 0:
GRUB_DEFAULT=0
This is the option that governs which GRUB menu entry to boot by default. Change it to the order of the option you want, eg.
GRUB_DEFAULT=3
Save the file ( duh! 😛 )
4. At the shell command prompt do a update-grub (as root) or use sudo:
$ sudo update-grub
You should see something like:
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.16.0-29-generic
Found initrd image: /boot/initrd.img-3.16.0-29-generic
Found memtest86+ image: /boot/memtest86+.elf
Found memtest86+ image: /boot/memtest86+.bin
Found Windows 7 (loader) on /dev/sdb1
done