I've just updated the files, look for the two files named "assembly" they contain all the parts for any changes you need.
.step and .iges are the standard extension for nurbs/solid models exchange.
If you can't still open them let us know and ask for a specific file format.
Anyway we're updating the model in these days because we got a stress fracture on the first version, so we'll keep you up to date for any improvement!
We're also dividing the main body in 2 separate parts to make it more printable on smaller 3D printers