Direct and Reported Speech

In the English language, there are two ways of conveying what someone else has said: direct/quoted speech and indirect/reported speech.
Direct/quoted speech, involves quoting the exact words uttered by the person, within inverted commas or quotation marks. For example: She said, “I won’t be coming home tonight” is an example of direct speech. Note that in this type of speech, a comma is most often used before starting the exact quote within the inverter commas.
Indirect/reported speech, on the other hand, does not have to be within quotes or reported word-to-word. In fact, unless one is relaying the exact words spoken, one should never use quotation marks. For example: She told us that she wouldn’t be coming home that night is an example of reported speech. Note that the verb tense necessarily changes in reported speech. This is because when we report speech, we are talking, obviously, about something that was said in the past. Hence, it becomes necessary to use the past tense of the verb.

DIRECT SPEECH	REPORTED SPEECH
He said, “I’m fine.”	He said that he was fine.
He said, “I’ve been married for three years.”	He said that he had been married for three years.
He said, “I went to the theatre yesterday.”	He said that he had gone to the theatre the day before.
He said, “The show was already underway when the chief guest arrived.”	He said that the show was already underway when the chief guest arrived. (no change in tense)

Another thing to note is that modal verbs (will, can, must, shall, may) also change, taking their past tense forms (would, could, had to, should, might). This also means that would, could, should, might and ought to do not change forms when reported.
 
Sumber :
http://www.englishleap.com/grammar/direct-and-reported-speech