This is the 7225th most frequent Japanese word.
下げる
To lower; to reduce; to bring down.
In this context, "下げる" means to lower or reduce something, specifically a price.
価格を下げることは売上を増やす方法の一つです。
Lowering the price is one way to increase sales.
Here, "下げる" is used to mean lowering or decreasing a measurable quantity, the room temperature.
部屋の温度を下げすぎると風邪をひくことがあります。
Lowering the room temperature too much might cause catching a cold.
In this case, "下げる" refers to reducing or lowering the volume or intensity, specifically the voice.