if you scale it either using mask or selection to isolate it, you should acheive desired result...
just remember to apply the scale (ctrl + a/scale) once you're satisfied with the result
Hey Mark,
sorry for that late answer of mine.
That was what I've already tried. Problem with this is, I didn't find out how to change the point from where it scales so it uses the origin point at 0/0/0. After fiddeling around a little I just went into edit mode, selected all the vertices and scaled them. That sucks a little because it leaves me with that rough transition between the scaled part and the other part, but I guess I have to go with it.
Regards,
tobles