A stackable washer dryer is really two appliances joined by a stacking kit. The safest way to move it is almost always to unstack the units and move them separately, because a stacked pair is too tall and top-heavy to handle safely.
Pro tip: Photograph the stacking bracket assembly before you take it apart so restacking is quick.
Watch out: Do not move the units while stacked. The combined height is dangerously top-heavy and the bracket is not made to bear transport loads.