How to change the booting sequence in BOSS4

open terminal
$ls -l /boot/grub/grub.cfg
OUTPUT will be like
-r--r--r-- 1 root root 5820 2010-08-12 03:03 /boot/grub/grub.cfg
give the write permission
$sudo chmod +w /boot/grub/grub.cfg
$ls -l /boot/grub/grub.cfg
OUTPUT will be like
-rw-r--r-- 1 root root 5820 2010-08-12 03:03 /boot/grub/grub.cfg

now open it in gedit
$sudo gedit /boot/grub/grub.cfg


search word "default", you will get a line like:
set default="0"

change it to
set default="1"
or
set default="2"
or
set default="3"
as per your choice.
1 to make second OS default
2 to make 3rd OS default
and so on
save it , close the window
remove the write permission:
$sudo chmod -w /boot/grub/grub.cfg
restart the system