It is very hard to explain novice users about making changes to some of the configuration files. Hence, I always keep digging into tools which helps us to make life easier. Especially on Ubuntu.
To make changes to GRUB default option, we need not tell users to edit the configuration when we have a tool called “grub-choose-default“.
First get it installed using following command on your terminal or by using Synaptic package manager.
sudo aptitude install grub-choose-default
Once this is done, you can execute the following command in terminal or via run prompt (Press Alt+F2 to get it ) to get the GUI tool to edit Grub Default .
Once you get this window, select the operating system which you want to boot by default. And you will be done with it.