A key change can lift energy, add contrast or mark a new section. Pop songs famously shift up a semitone or a whole tone for the final chorus. Classical forms modulate to related keys, such as the dominant, and return home at the end.
Smooth modulations use a pivot chord shared by both keys. Sudden ones, called direct modulations, jump without preparation for a bigger effect.
Using it in a prompt
Say "key change up a step for the final chorus" when you want that classic lift. It works well in gospel, pop and wedding music.