Quoting Suresh Raja sureshraja.cu@gmail.com:
Could someone update the GNU Octave in the EPEL repository to the current version 3.6.4?
Can't. The EPEL6 branch is at 3.4.3, and a version upgrade is not really allowed in the EPEL guidelines.
Once EPEL7 gets out, it will feature the then-newest version of Octave.