Upgrade from PostgreSQL 9.5 on Ubuntu 16.04 to PostgreSQL 10.3 on Ubuntu 18.04

sudo apt install -y postgresql-10

// upgrade
sudo pg_dropcluster 10 main --stop
sudo pg_upgradecluster 9.5 main

// check
pg_lsclusters 

// remove
sudo pg_dropcluster 9.5 main
sudo apt remove -y postgresql-9.5