Currently if I select a group of object and change the Z value it only move the object I originally selected. Is it possible to change the coordinates of a certain selection of objects of different Z values to all the same Z values without changing the x or y values. In addition to this can you change the selection of objects height without changing their width or length. If either of these are possible then how is it possible. If possible could you tell me in the simplest way possible as I don't know much about blender.
Place one of the objects at the height you need. Then select all the objects again, making sure you select the "right height object" last so that it's the active one. Then go to Object/Transform/Align Objects, and activate Z axis.
PS - I'm in Blender 2.79, and the Alt key doesn't work the same way.