How I can update my octave-3.2.4 to octave-3.6.2?
Besides installing the upstream version from source, you have a couple other options.
Install From Quantal Packages
Octave 3.6.2 is packaged for Quantal (the upcoming Ubuntu release). It might (usually does, sometimes doesn't) work to manually download those packages.
Use a PPA
You may be able to find Octave 3.6.2 pre-built for the Ubuntu release you're currently running, provided by an unofficial PPA. If so, this may be the best way to install it. But please read this first so you know about possible dangers from PPA's.
You can find some PPA's that provide Octave (though it won't necessarily be an exhaustive list) by going to the bottom of this page and clicking the green link that says "Other versions of 'octave' in untrusted archives."
You can enable this PPA and install Octave from it by running these commands in the Terminal: