"좋은 하루 보내세요" Joh-eun haru bonaeseyo. [Have a nice day] "즐거운 하루 보내세요" Jeulgeo-un haru bonaeseyo. [Have a pleasant day] "즐겁게 지내세요" Jeulgeob-ge jinaeseyo. [Let (your day) be pleasant] Informally (not a polite form), you could maybe say: "좋은 하루 보내라" Joh-eun haru bonaera. (towards a good friend) Sometimes people say: "좋은 하루 되세요", (Joh-eun haru doeseyo) but I read that this is not correct. I don't know.