ubuntu-change-hostname

Summary:

sudo hostname NEW_NAME_HERE
sudo nano /etc/hostname # change OLD_NAME by NEW_NAME
sudo nano /etc/hosts # change OLD_NAME by NEW_NAME
sudo systemctl restart systemd-logind.service
hostnamectl set-hostname NEW_NAME_HERE
Also you should recreate your ssh keys on your machine:

sudo rm /etc/ssh/ssh_host_*
sudo dpkg-reconfigure openssh-server
Just in case, check references of your old hostname on /etc and fix it:

sudo grep -R pulex /etc/ 2>/dev/null