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

Tense change

As a rule when you report something someone has said you go back a tense: (the tense on the left changes to the tense on the right )

Direct speech Indirect speech
Present simple 
She said, “It’s cold.”
Past simple 
She said it was cold.
Present continuous 
She said, “I’m teaching English online.”
Past continuous 
She said she was teaching English online.
Present perfect simple 
She said, “I’ve been on the web since 1999.”
Past perfect simple
She said she had been on the web since 1999.
Present perfect continuous 
She said, “I’ve been teaching English for seven years.”
Past perfect continuous 
She said she had been teaching English for seven years.
Past simple 
She said, “I taught online yesterday.”
Past perfect 
She said she had taught online yesterday.
Past continuous 
She said, “I was teaching earlier.”
Past perfect continuous 
She said she had been teaching earlier.
Past perfect 
She said, “The lesson had already started when he arrived.”
Past perfect 
NO CHANGE – She said the lesson had already started when he arrived.
Past perfect continuous
She said, “I’d already been teaching for five minutes.”
Past perfect continuous 
NO CHANGE – She said she’d already been teaching for five minutes.

Modal verb forms also sometimes change:

Direct speech Indirect speech
will
She said, “I’ll teach English online tomorrow.”
would
She said she would teach English online tomorrow.
can
She said, “I can teach English online.”
could
She said she could teach English online.
must
She said, “I must have a computer to teach English online.”
had to 
She said she had to have a computer to teach English online.
shall
She said, “What shall we learn today?”
should
She asked what we should learn today.
may
She said, “May I open a new browser?”
might
She asked if she might open a new browser.