What are the differences in aesthetic designs change and functional changes?

aesthetic changes in car and other vehicles are simply changes to the shape of the body, such as making it more pleasing to look at and draw people into buying the car. This would be called face-lifting i believe.

Functional changes are changes that would actually change the performance of the car, for example the body of the car may be changed so as to create more downforce, to get more power out of the engine, developing more advanced suspension systems etc.