How does a hot air balloon pilot ascend and descend?

A hot air balloon pilot ascends by heating the air inside the envelope using a burner, which makes the air less dense than the cooler air outside, causing the balloon to rise. To descend, the pilot can either allow the air to cool naturally or use a vent at the top of the envelope to release some hot air, increasing the balloon's density and causing it to descend. The pilot controls both ascent and descent by carefully managing the temperature of the air inside the balloon.