New deployments of 12.04.2 will be installed with an updated kernel and a new X windows stack.
For existing 12.04 deployments, users will need to opt-in to what is being called the LTS Hardware Enablement Stack. If you already have Ubuntu 12.04 installed with an earlier kernel stack, it is recommended that you keep this stack in place rather than switching to a later kernel; the newer kernel and X stacks are provided for enablement of hardware not supported by earlier kernels, and there is generally no reason to upgrade to a newer stack if your hardware is supported by the default kernel.
In order to upgrade to the 3.5 kernel on 12.04.2, you will need to run the following command(s):
For the new kernel:
sudo apt-get install linux-generic-lts-quantal
For the new X stack:
sudo apt-get install xserver-xorg-lts-quantal
WARNING: If you are using the xorg-edgers PPA, do not install the xserver-xorg-lts-quantal package as this will most likely result in breakage.
This is only recommended for x86 hardware installations.