As you might know, 상 means "up" and 하 means "down". Also 상 and 하 are used for denoting a volume of book or movie or something else. So, 상 means "first volume" and 하 means "last volume" If a novel is consist of two volumes, 상 means "volume 1" and 하 means "volume 2" If a novel is consist of three volumes, 상 means "volume 1" and 중 means "volume 2" and 하 means "volume 3" It also can be used for chapters of book. If a chapter is too long, it can be divided into some parts with same title. I guess the chapter 화이트데이 거북이 사탕 is too long for one chapter. 화이트데이 거북이 사탕(상) means "화이트데이 거북이 사탕 first part" 화이트데이 거북이 사탕(하) means "화이트데이 거북이 사탕 last part"