When the energy is transformed, the total energy changes.

Law of conservation of energy states that, “Energy can neither be created nor be destroyed. It can be transferred from one form to another.” Hence, the total energy of the system remains the constant and doesn't change.

Consider a ball at a height, the potential energy of the ball is maximum at the maximum height while the kinetic energy is zero. When the ball starts falling down, with the decrease in height, the potential energy decreases and kinetic energy increases due to the increase in the velocity of the ball. When the ball reaches the ground, the potential energy reduces to zero while the kinetic energy gets maximum. hence, the total energy of the ball doesn't change and remains constant.