Updating to Ubuntu 18.04
This guide will show you how to upgrade to the latest version of ubuntu
Login via VNC and then run the below commands
apt update && apt dist-upgrade
apt install update-manager-core
Next,
do-release-upgrade
If that didn't work, try:
do-release-upgrade -d
Hit 'N' and enter
once the update is complete, login again and run the following commands:
apt autoremove
apt update
apt dist-upgrade
And update should be done