Ubuntu 12.04 is a Long Term Support release. This means that the version of Apache included with it will continue to receive security updates into 2017. So while you might not have the most recent version installed, security patches are backported to your version. So you shouldn’t necessarily be concerned that you don’t have the latest.
When making upgrades to a major piece of software like Apache, you risk making your system unstable. One of the main reasons for using a distribution’s package management system rather than installing the latest upstream software is that you get a set of packages that have been tested together. If you update one outside of the package management system, you may introduce incompatibilities. This can particularly be a problem if you rely on non-default Apache modules.
If you really need a more recent version of Apache, I’d suggest upgrading to Ubuntu 14.04. If you don’t want to do that, you can still get a more recent version by enabling this PPA:
sudo add-apt-repository ppa:ondrej/apache2
sudo apt-get update
sudo apt-get dist-upgrade