This is a guide on how to upgrade Postgres. The commands below will install a new Postgres 9.6 instance, migrate all the data, and afterwards uninstall the old Postgres 9.5 instance.
Note: I've used these exact commands on Ubuntu 16.04. Your mileage may vary on other OSes and Postgres versions.
1. Install the new version
sudo apt-get install postgresql-9.6
2. Make sure both version are installed and running
sudo pg_lsclusters
The output should be something like:
Ver Cluster Port Status Owner Data directory Log file
9.5 main 5432 online postgres /var/lib/postgresql/9.5/main /var/log/postgresql/postgresql-9.5-main.log
9.6 main 5433 online postgres /var/lib/postgresql/9.6/main /var/log/postgresql/postgresql-9.6-main.log
3. Migrate the data from old to new
Your ports may be different, check the previous command's output.
sudo -u postgres -i
pg_dumpall -p 5432 | psql -d postgres -p 5433
exit
4. Update the ports
Open postgresql.conf and set the port value of the 9.6 instance in to 5432. If you're going to keep the 9.5 version, also set its port to some other integer (e.g. 5433).
sudo vim /etc/postgresql/9.5/main/postgresql.conf
sudo vim /etc/postgresql/9.6/main/postgresql.conf
5. Uninstall the old version (optional)
sudo apt-get purge postgresql-9.5
6. Ensure the new version is up
Make sure the port is set correctly.
sudo service postgresql start
sudo pg_lsclusters