For the second part, if the electric field is constant and is along the z-direction, the equipotential surfaces are the planes parallel to the xy plane. Let us say that there are three equally spaced planes with potentials 3V, 2V & V respectively as z increases (this gives us constant potential gradient, i.e. constant field). For the first part, if the field is in the same direction i.e. z-direction then the equipotential surfaces are planes parallel to the xy plane again. In this case if three planes are drawn having potentials 3V, 2V and V respectively as z increases then these planes would not be equally spaced now because now we want increasing electric field. The spacing between them needs to decrease to give increasing electric field.