Just a few steps. Let's start!

this step without GUI Application

1. Open ur terminal (shortcut: CTRL+ALT+T)
2. type this command to let u know menu entry for ur grub

grep menuentry /boot/grub/grub.cfg

if ur laptop/pc dual booting with Windows, the output should be like this:


know ur windows name:


3. make copy ur file with this command:
cp  /etc/default/grub /etc/default/grub.bak

4. edit ur default grub with run this command
nano /etc/default/grub

the output should be like this:



focus on line below:


edit like this:



u can change grub timeout by replace this code:


5. save ur work and update ur grub with this command:
update-grub
and the output should be like this:


and the last step is reboot ur laptop/pc
reboot

thanks for reading
any question? just comment