One of the main ideas of the quantum theory is that:

the energy of an electron can never be changed

the energy of an electron can be varied by any amount

the energy of an electron can be changed only by set amounts

the energy of an electron can always be predicted with 100% accuracy

The energy of an electron can be change only by set amounts.

The electrons in an energy level of an atom can only move to a higher or lower energy level only if it absorbs or emits a certain amount of energy. If the electron does not have enough energy to move to the next energy level then it will never move.