1
general::
Phrase(s): change the subject
to begin talking about something different. • They changed the subject suddenly when the person whom they had been discussing entered the room. • We’ll change the subject if we are embarrassing you.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Deliberately talk about another topic, as in If someone asks you an embarrassing question, just change the subject. This term uses subject in the sense of "a topic of conversation," a usage dating from the late 1500s.
American Heritage Idioms