They used to sell Basic 8 for the C128 as a Rom chip that you could put into the C128 expansion rom socket or you could put it in your REU expansion socket. For plain old C64, there were carts that added commands and shortcuts to basic like Simon's Basic, Super Expander and S'more. Other than that there is no way to "upgrade" C64 basic. Why are you looking to upgrade it by the way?
