A ceiling fan does not change the actual ambient temperature of a room. What it does do, is move or distribute air. This has several interesting implications;
From a cooling perspective in Summer, by directing a downdraft onto a person, a fan creates a breeze which has a cooling effect by evaporating body moisture to make one feel cooler and more comfortable.
From a warming perspective in Winter, a fan circulates the air in a room to distribute the warm air that has risen and may be trapped in the ceiling area. By doing this, it raises the temperature of the air at the lower levels and makes one feel warmer.