#1- Delete the old name and setup new name
sudo hostnamectl set-hostname newHostname
#2- Edit the /etc/hosts file:
sudo nano /etc/hosts
#3- Reboot the system
sudo reboot
#4- To check the new hostname
hostnamectl
change hostname ubuntu 20.04
#Change hostname
sudo hostnamectl set-hostname newHostName
#Edit the /etc/hosts file, and replace existing hostname with a new hostname.
sudo nano /etc/hosts
#Reboot the system to changes take effect
sudo reboot