Unable to update Octave version in Lubuntu 16?

[IMacaulay]

I see that the most recent version is showing as 4.2.1, but when I
have tried to update using

> sudo apt-get install octave

I get

  octave is already the newest version (4.0.2-1ubuntu5~octave~xenial1).

Any suggestions for updating my Octave, please?  My system is Lubuntu
16.04.2 LTS (kernel is Linux 4.4.0-72-generic (x86_64)).

Thanks.