change your default system opening option using Ubuntu

There are lots of tutorials but I still met some troubles, so I make a quick tutorial.

There  are 5 clearly steps to change your turning on default system:

1.open your Terminal and input:sudo  gedit /etc/default/grub

2.change the GRUB_DEFAULT=0 to GRUB_DEFAULT=4(if you want to enter the fifth option,count from 0) in grub file 

3.save it

4.close it 

5.input sudo update-grub

tips:

1.sudo will authority you changing the grub file, without sudo you can't change it and update it.

2.you need to close the grub file so you can update it.