"Change down" is a term usually used in the context of driving, referring to the process of shifting gears to reduce speed. Some synonyms for this term include downshift, gear down, and shift down. Other possible expressions can include decelerate, slow down, come to a stop, and reduce the speed. These terms can be used depending on the context or situation, but they all denote a process of decreasing speed or momentum. It is always advisable to use the appropriate terminology in each specific context, especially in matters concerning safety.