We change direct speech to reported speech by shifting phrase's tense by one in time. Present tenses (Present simple, Present continuous, Present perfect and Present perfect continuous) become their past equivalents (Past simple, Past continuous, Past perfect and Past perfect continuous), Past simple becomes Past perfect and 'will' in future tense becomes 'would'. Past perfect tense doesn't change.

Aside from that, certain words, time expressions and pronouns change (so that they mean the person referred to in direct speech).