postgresql 删除旧的版本9.5 并同时 升级到9.6

sudo apt-get purge postgresql-9.5

On Ubuntu 14.04 I have done this to get the latest postgres:

sudo sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt/ $(lsb_release -cs)-pgdg main" > /etc/apt/sources.list.d/pgdg.list'
wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -
sudo apt-get update
sudo apt-get upgrade

Then I installed version 9.4:

sudo apt-get install postgresql-9.4

However it seems I have now three versions:

sudo service postgresql stop

 * Stopping PostgreSQL 9.3 database server  [ OK ]
 * Stopping PostgreSQL 9.4 database server  [ OK ]
 * Stopping PostgreSQL 9.5 database server  [ OK ]

How can I keep only 9.4 and uninstall the other ones? Thanks

UPDATE:

As suggested in comments I have uninstalled 9.3 and 9.5.

But when I do this:

sudo service postgresql status
9.3/main (port 5432): down
9.4/main (port 5434): online
9.5/main (port 5433): down

So far so good, but when I switch to postgres:

sudo su postgres

and do a psql, I get an error:

psql: could not connect to server: No such file or directory
    Is the server running locally and accepting
    connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

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Different versions of PostgreSQL are located in the packages postgresql-9.*.

1. So you should remove your two packages:

   sudo apt-get purge postgresql-9.3 postgresql-9.5
   

2. Then you should remove unnecessary config folders:

   rm -r /etc/postgresql/9.3/ /etc/postgresql/9.5
   

3. And from /var/lib/ folder if you have:

   /var/lib/postgresql/*
   

I hope it will help you.