My first hunch, in the abscense of a ~.blend file, is that the head and the body are separate objects, and that at some point you moved the head in edit mode when you should have moved the head in object mode. Moving the head in edit mode moves the vertices, but not the object's origin, but the object is rendered based on the objects origin. The solution (assuming the origin is in the proper place) is to select edit mode, if you're not already in that mode, select the head object and press the key combination CTRL - ALT - SHFT - C, and select the option "geometry to origin". If the origin is not in the right point, you'll want to move the origin to where it is, before moving the geometry to the origin. After you have the origin and the geometry in the proper location relative to where you want them, you'll enter object mode and apply the location using the combination CTRL - A.