follow official guide
$ echo "deb http://apt.postgresql.org/pub/repos/apt/ precise-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 install postgresql-9.3 postgresql-contrib-9.3you should succesfully installing postgresql 9.3.2 on your machine.
but, if you have same problem like me.
The following packages have ummet dependencies:
  postgresql-9.3 :  Depends: postgresql-client-9.3 but is not going to be installed
                    Depends: postgresql-common (>=1.4.2)...
  ...you should install postgresql-common with specific version like this:
$ sudo apt-get install postgresql-common=151.pgdg12.4+1
$ sudo apt-get install postgresql-9.3 postgresql-contrib-9.3
Had to do the same procedure for the package
postgresql-client-common. Then did it forpostgresql-commonand postgres installed fine after that.Thank you!