If all you're looking to do is get some security updates, then don't worry about it - as long as you have a standard installation and you run:
You'll get the updates from the karmic-security APT repository. It's Ubuntu's policy to not change the version of a package once released, but they will backport security updates from later releases as necessary. There are a handful of exceptions to this policy (Firefox being the most notable) but Apache2 isn't one of them.
In fact, if you look at the apache2 karmic package page, you'll see the current version is noted as "security" and if you view the changelog you'll see they've already backported the security issues.
If you're really interested in getting a later version without upgrading, you should read the Ubuntu Backports wiki page. There are a number of different options available, from re-building your own packages to using the Ubuntu backports repository to get some later packages.