How do I replace bootloader to grub from mbr?

Question

I want the system to boot directly into ubuntu.

I have tried the solution:

1. How to set grub as the boot manager?

2. Remove windows boot manager and use grub instead

3. How to get GRUB to be the default bootloader instead of Windows Boot Manager on a UEFI laptop?

4. https://superuser.com/questions/1247300/how-to-make-uefi-bios-start-grub-not-windows

but I failed.

I have dual boot windows 10 and Ubuntu 18.04 LTS.

Now its booting into windows 10 if I don't press any key.

I want it to boot the system to Ubuntu.

Thanks