GrUbUbUnTu12.04

It's still the same thing

sudo gedit /boot/grub/grub.cfg

U could change this lines if you want to change the SO

set default="x"
set timeout=10 shows time out to inicialize your SO

In each case you should to choose the SO that you want to Inicialize.
If u want to initialize with Ubuntu 12 just do this:

set default="0"

U can see the number that u need in the boot menu the first one in 0, the below one is 1, 2, 3, 4, 5, 6.
If the computer have more than 1 user and some one doesn't know how to use Ubuntu and doesn't like that the computer have 2 SO, u can do this:

set default="6"
set timeout=1