edit grub background and timeout , default os ubuntu 20.04

change grub image background and the timeout without extra software on ubuntu 20.04 :
-copy your image background to : /boot/grub
-edit timeout seeting: sudo nano /etc/default/grub
-edit your os nummber

after edit :
ctr + O
entry
ctr + X

-update your grub: sudo update-grub

[AabhaasDeshta]

sudo update-grub after this there is an error Sourcing file `/etc/default/grub'
/usr/sbin/grub-mkconfig: 30: /etc/default/grub: menuentry: not found