Datum

With harddisk space it is the same thing like with RAM or with the engine size of your car: it can only be replaced with one thing. More of it.

If you want to know where your diskspace went to, where are some good tools that give an overview of the disk usage. Two good tools that do that, including graphical representation of direcories and files are the following:

Linux

baobab is part of every GNOME desktop.

Windows

TreeSize Free