Ubuntu 18.04 and 16.04 How to change the resolution

1. open

sudo gedit /etc/default/grub

2. Find

#GRUB_GFXMODE=640x480

3. Replace the above line by the following line

GRUB_GFXMODE=1920x1080 

4. update command

sudo update-grub

5. restart your system

sudo reboot