I've changed position of vertices with python but nothing happened I'm really newbie at blender. So I want to change an object from a python script.

If I create a new project (Ctrl+N) and open python console, I can changing position of vertices:

bpy.data.meshes['Cube'].vertices[0].co.z += 20


But if I'm using .blend file with mesh from here:
http://www.blender-models.com/model-downloads/humans/id/head-mesh/
I can changing vertices too

but I don't see anything new at 3D view window.


What I'm doing wrong.
Please try your statements with the 3D View Window in object mode not edit mode.