Answer by Correcter for How to uninstall specific versions of Postgres?

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.