In 1984, people like Winston rectify old records that have been proven false, or in other words the government does not agree with them.
Winston lives in a dystopia where every citizen is watched constantly by the government of Big Brother, children spy on their parents, and thinking is a crime. The country of Oceana is perpetually at war with Eurasia.
Winston works for the Records Department, which is a department of the Ministry of Truth. His job is to rectify records so that they match what the government wants them to say.
Today’s issue contained a statement of the actual output, from which it appeared that the forecasts were in every instance grossly wrong. Winston’s job was to rectify the original figures by making them agree with the later ones. (part 1, ch 4, p. 23)
Orwell shows us a world where people have no freedoms, and the government says whatever it likes and does whatever it likes. This is Orwell’s vision of the future, where we are watched constantly by Big Brother Government. It is a world of doublethink and doublespeak, where nothing that is said can be trusted. Let this story be a warning to us all.
The answer to this question is that the official term for altering records is "rectifying."
You can find the answer to this question right at the beginning of Chapter 4. In that chapter, we see Winston at work. His work is to take the bits of news that are no longer acceptable and to change them.
For example, he has to retrieve an article in which Big Brother made a predicition about the war that turned out to be wrong. All that he has to do there is to rewrite a paragraph of the speech so that it will look like Big Brother predicted what actually did happen.