Reported speech

  Reportedspecch is report what another person has said, we usually do not use the speaker’s exact words (direct speech), but reported (indirect) speech. Therefore, you need to learn how to transform direct speech into reported speech. The structure is a little different depending on whether you want to transform a statement, question or request.

Speker word's example :

Direct speech		Indirect speech
Present simple	›	Past simple
Present continuous	›	Past continuous
Present perfect simple	›	Past perfect simple
Present perfect continuous	›	Past perfect continuous
Past simple	›	Past perfect
Past continuous	›	Past perfect continuous
Past perfect	›	Past perfect
Past perfect continuous	›	Past perfect continuous

Modal verb forms also sometimes change:

Direct speech		Indirect speech
will	›	would
can	›	could
must.	›	had to .
shall	›	should
may	›	might .

Sumber : http://www.learnenglish.de/grammar/reportedspeech.htm