14.04.2 and 14.04.3 are not "releases" in terms of "do-release-upgrade".
"Point" releases accumulate security updates and bug fixes that are added to Ubuntu repositories.
If you install ordinary updates on Ubuntu 14.04, 14.04.1 or 14.04.2, you will get 14.04.3.
So your goal makes no sense.
The only difference of the ISO of the point releases is HWE Stack. Kernels are updated to another major version and xserver.
If this is your question you can install 3.16 kernel and graphical stack of 14.04.2 by running
sudo apt-get install linux-generic-lts-utopic xserver-xorg-lts-utopic libqt5gui5 libgles1-mesa-lts-utopic libgles2-mesa-lts-utopic libgl1-mesa-glx-lts-utopic libgl1-mesa-glx-lts-utopic:i386 libglapi-mesa-lts-utopic:i386 libegl1-mesa-drivers-lts-utopic
The command given in the official wiki can brake your system in some cases.