rename computer ubuntu 20.04

C++
#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
hostnamectlusermod -l <newname> -d /home/<newname> -m <oldname>
Source

Also in C++: