Kernel 3.5.x is the default kernel for installs of v12.04.2 version of Ubuntu. This is logically the only way you could have this kernel series unless someone manually installed this kernel as part of the hardware-enablement-stack (explained below) - you cannot via a normal
sudo apt-get update etc.
This is explained in the release notes
In an effort to support a wider variety of hardware on an existing LTS
release, the 12.04.2 point release will ship with an updated kernel
and X stack by default. This newer hardware enablement stack will be
comprised of the kernel and X stack from the Quantal 12.10 release.
The readme continues to explain if you want to stick with the default 3.2.x series:
Install from a previous 12.04.0 or 12.04.1 point release and update.
The previous 12.04.0 and 12.04.1 releases are archived at
http://old-releases.ubuntu.com/ Perform an update or upgrade to
Precise from a previous Ubuntu release. Only those installing from the
12.04.2 media will automatically receive a newer hardware enablement stack by default.
Perform a network install using the netboot images rather than the new
Note - the current version of Ubuntu is 12.04.3 - this comes with the 3.8 kernel series (i.e. the raring kernel).
Naturally, this being Ask Ubuntu - we have great questions that explain how to uplift your older Ubuntu installs to newer kernels:
-How to upgrade 12.04.2 kernel and HWE to raring?
The answer is equally applicable to older ubuntu versions.
You should be aware, you dont need to install the newer kernels - the older 3.2.x series is supported for the full 5 year support period.
This is explained also in the community wiki about the hardware-enablement-stack