Q:

After upgrading to Ubuntu 19.04 from 18.10 always showing the GRUB window. How can I fix it?

I have upgraded Ubuntu from 18.10 to 19.04 but after that the GRUB is always showing.
Note: In my machine I'm only using Ubuntu.

A:

I got an temporary solution and applied. Now GRUB window is not showing.
The solution is:

Delete old kernel: I have deleted old kernel 4.18 by using Synaptic. link
Set GRUB_TIMEOUT = 0 at sudo gedit /etc/default/grub

