I have Ubuntu and Fedora installed, and I'd like to format and do a fresh install.
 

I've got an 8GB netbook, so I don't have much space. I need to run a fractal-generating software for school, but I don't have enough space. I've got a lot of crap on my computer, and I've already copied everything I need onto a USB memory stick.

I've got Fedora installed and Ubuntu installed twice, sicne I thought that every installation over-wrote the previous one, so there's a lot of crap I never use on my computer. Now, I'd very much like to install the new version of Ubuntu (Karmic Koala, right?) and get rid of all he crap that's clogging up my computer. I don't think this is a hard problem to solve, but it's really urgent, and I don't know an awful lot about Linux. So, think you could help me out?

So just do a fresh install. What's your problem ?

But, if I install Ubuntu 9.04, won't Fedora and all my settings still be there? How do I format them?

You can select to format all your partition completely while installing Ubuntu 9.04. Nothing will remain then.