Complex sentence: To change the color of such a radiating body it is necessary to change its temperature, and increasing its temperature changes the quanta of energy that are available to excite individual atoms to higher levels and permit them to emit photons of higher frequencies.
Split into simpler sentences: To change the color of such a radiating body it is necessary to change its temperature. An increase in temperature changes the quanta of energy available to excite individual atoms to higher levels, enabling them to emit photons of higher frequencies.