yum install http://yum.postgresql.org/9.4/redhat/rhel-6-x86_64/pgdg-redhat94-9.4-1.noarch.rpm
Once this is done, you can proceed to install and update packages the same way as the ones included in the distribution.
yum install postgresql94-server postgresql94-contrib
service postgresql-9.4 initdb
chkconfig postgresql-9.4 on