Is to possible to enlarge disc space for my Ubuntu partition?

I’ve installed ubuntu with the 7gb option, but I’d like to give it more available space. I’ve got plenty enough for the 30gb installation on the hd available, but is it possible to ‘enlarge’ the space dedicated to ubuntu once it’s been installed?
Or must I go to windows, use Wubi to erase my current installation and reinstall it with the desired amount of Gb space? And in this last case, is there a way to clone my current Ubuntu partitioned installation (to use it in the further installation I might have to do)?