I'm pretty sure Moini means the directory which is showing in Inkscape Preferences > System > User config. The pathway to that directory is different, depending on which operating system you use. So we refer you to look there, rather than remember what it's called for the 3 major systems.
Anyway, once you get there, look for the templates folder. That's where default.svg will be.
I'm curious which operating system you use, and which version of Inkscape you tried to install. Depending on which system, and which version you had previously installed, it might be important to uninstall it, before installing the new one.
I would start right off by uninstalling whatever you installed. Then double-check you downloaded the correct package, and try again.
If you still see the same problem, then look up the default.svg template