Although normal software updates will bring your system up to 12.04.3, the Hardware Enablement Stack (HWE; the *-lts-raring packages) is not part of those updates (by policy).

You can install the HWE packages manually, but there are some caveats.

To upgrade use this command line only:

sudo apt-get install --install-recommends xserver-xorg-lts-raring

The --install-recommends is important. It makes sure that the xserver will install completely. Without it, xserver will only install partly, and apt will remove most of your system. You do not need to add linux-generic-lts-raring, as it is already recommended by the xserver package, and the Kernel 3.8 will install too.

When you upgrade like this you may notice that there are configurations left over, among others those of the original xserver-xorg. You can purge them (I always do), but beware: this will remove the symlink /etc/X11/X that is used to start the XServer, so on next boot it won't start. To prevent this, after purging left over configurations, do the following before the next boot:

sudo dpkg-reconfigure xserver-xorg-lts-raring

This will recreate the necessary symlink and everything is fine again.