Hi Glenn Claes,

Try this method, it should work.

1) Select your part
2) Unjoin all its surfaces
3) Show control points of all selected surfaces
4) press "Esc" to deselect every surface
5) select the desired control points
6) move them to do the modification you need
7) press "Esc" to exit control point editing mode
8) re-select all the object's surfaces
9) Join all together to obtain a solid again

I think that if your model is simple this steps should work.

Nice Day,

Marco (mkdm).