:- Forward biasing increases the electron density in the conduction band of the n-side. As a result the fermi level moves upwards. Similarly due to the increase in the hole density in the valence band of the p side , the fermi level moves downwards. The fermi levels and are displaced relatively by an amount eV equal to the potential energy due to the applied voltage, V which cause the displacement. The height of the conduction hill reduces by the same amount eV and becomes $e(V_o-V)$. Similarly the height of the valence hill becomes $-e(V_o-V)$. This makes the charge flow through the junction easier.