Well, it's been a while since I used Ubuntu, I now use Kubuntu. Assuming you really really need the very latest version because some feature is missing from what you already have.
I believe under under software sources on the updates tab there is an option to turn on pre-release updates (your's would show maverick instead of lucid). So click on that, apply it and do an apt-get update.
Alternatively, I think you can also edit /etc/apt/sources.list directly and follow the comments. In mine I can uncomment a couple of lines to get those repositories (which is what the tick box in the dialog shown would do).
If that doesn't get you the latest build, you could also download the apache sources yourself and compile them. You may need to apt-get install gcc and apt-get install g++ and anything else it depends on. However, you'll be on your own when it comes to maintaining. To upgrade you'll have to compile from sources all over again.
Compilation is not that hard. It's usually just a matter of doing something like:
sudo make install
There may be some options you'd want to supply to ./configure. ./configure --help shows them. But read the apache compilation documentation before you start. Again, assuming you really really need the very latest version and you're prepared to go down this route.
And despite the comment below. The above will work fine. See: compiling for the impatient.