Holography, in short, is a science of recording the light waves of a laser reflected off of an object. The holographic film records an infinite number of views of the object, whereas a photograph records only one view. Thus, when viewing a hologram, our left eye sees a different apparent view of the object than our right eye, and the image appears three dimensional.
Most holographic techniques produce images which are identical in size to the original object.
There are new developments which allow some enlargement and reduction if necessary. Yes, but the laser recording will recreate only what it sees. A hologram created from flat art looks quite different from the astounding, fully dimensional image created when a hologram is made from an object or sculpture. Yes, to some extant you can.