Ubuntu LTS releases, like 14.04 are supported for many years. However, the kernel and X server that ship with them are only updated for minor changes or revisions during this period. Every six months Ubuntu puts out a new point release for its recent LTS, like 14.04.2. This has the kernel and X server from the most recent Ubuntu non-LTS release.
The Ubuntu LTS Enablement Stack provides these updated Linux kernels and X server releases for users running older LTS releases. For computers with NVIDIA graphics cards, I have found that switching to newer kernel and X server has always improved the driver errors I face.
The LTS Enablement Stack webpage has the charts of what kernel and X server versions are available for your LTS release. You can also find the command to update your LTS from there.
For example, I updated my 14.04 system using this command:
$ sudo apt-get install --install-recommends linux-generic-lts-vivid xserver-xorg-core-lts-vivid xserver-xorg-lts-vivid xserver-xorg-video-all-lts-vivid xserver-xorg-input-all-lts-vivid libwayland-egl1-mesa-lts-vivid
My kernel was updated from 3.13 to 3.19 after this. Remember to reboot after this command! 😄
Tried with: Ubuntu 14.04