sudo service postgresql stop
sudo apt-get install postgresql-9.6
sudo service postgresql staus
sudo service postgresql start

dump all the data

pg_dumpall >9.5.db

fix pg_hba

if you try to connect

    psql -p 5433 -U postgres

will get error

    FATAL: Peer authentication failed for user "postgres"

check http://stackoverflow.com/questions/18664074

the problem is still your pg_hba.conf file (/etc/postgresql/9.1/main/pg_hba.conf). This line:

local   all             postgres                                peer

Should be

local   all             postgres                                md5

after change the config

psql -p 5433 -U postgres -f  9.5.db
sudo service postgresql stop
sudo apt-get purge postgresql-9.5

and then, chage peer to trust, and the change back to ‘md5’

finally, restart to db

sudo service postgresql start