sudo sed -i 's/Prompt\=lts/Prompt=normal/g' /etc/update-manager/release-upgrades
sudo sed -i 's/bionic/disco/g' /etc/apt/sources.list
sudo sed -i 's/bionic/disco/g' /etc/apt/sources.list.d/*.list
sudo sed -i 's/18\.04/19.04/g' /etc/apt/sources.list.d/*.list
sudo apt update
sudo apt upgrade
sudo apt dist-upgrade
sudo apt autoclean
sudo apt autoremove
That's all! See you.