If the reporting verb is in the past form (said, told...), you must change the tense.

Example: 

Peter said, "Carol is a nice girl." Peter said (that) Carol was a nice girl.

When you form the reported speech, you must pay attention that the pronouns refer to the correct person.

Examples: 

• Susan said, "My parents are amazing doctors."
• Susan said (that) her parents were amazing doctors.

•             Tom said, "I like black cars best."
•              Tom said (that) he liked black cars best.

•      They said, "We went swimming with our friends."
•             They said (that) they had gone swimming with their friend.

•   Jack said, "David told me the truth."            
• Jack said (that) David had told him the truth.

Direct  speech Indirect speech

She said I - my - me she - her - her

He said I - my - me he - his - him

They said they - their - them we - our - us

Expressions of time and place must also be changed.

Example: 

• She said, "I have already seen Carol today." 
• She said (that) she had already seen Carol that day