To install PostgreSQL 9.3 I used the following steps as root:
echo "deb http://apt.postgresql.org/pub/repos/apt/ `lsb_release -c | awk '{print $2}'`-pgdg main" > /etc/apt/sources.list.d/postgre.list &&
wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add -
apt-get update && apt-get dist-upgrade && apt-get install postgresql-9.3