One simple example is found when the pigs decide they want to move into the farmhouse or to assume other privileges that the other animals cannot. They have to keep themselves comfortable so that they can do the great work they are called upon to do. They have to eat apples and drink the milk because otherwise they would lose their strength and be unable to perform the tasks they've chosen for themselves. Of course they also suggest that they "don't even want to take the apples" but they must as they consider the demands placed on them.
Another example is their revision of the sixth commandment to never kill another animal. The pigs have to change it to justify their executions so they simply add "without cause" to the end. And eventually they try to erase any memory of the original.
There are lots of example where Napoleon and Squealer change the truth and manipulate the other animals :
-the best example is how they make Snowball looks like a big traitor, after Napoleon gets rid of him Squealer tells the other animal that he was "no better than a criminal" and they finally beleive Squealer .When the windmill is in ruin because of the tempest Napoleon accuses him (" Snowball has done this thing! In sheer malignity, thinking to set back our plans and avenge himself for his ignominious expulsion, this traitor has crept here under cover of night and destroyed our work of nearly a year...") and sentences him to death as a punishment for his behaviour.
-as said above Squealer and N. also change the Seven Commandment; for example they change the moto "No animal shall kill any other animal " to " No animal shall kill any other animal without cause" and to explain those facts they blame the 'faulty' memory of the other animals:"Somehow, or other, the last 2 words had slipped out of the animal's memory.." . There are lots of other example like this one ...
-The other thing that Squealer does is to lie to them when saying that they are more prosperous, work less, had a better condition of living ...in brief a better life now than with Mr Jones ("He proved to them in detail that they had more oats, more hay, more turnips than they had had in Jone's day, that they worked shorter hours, that their drinking water was of better quality, that the live longer, that a large proportion of their young ones survived infancy, and that they had more straw in their stallls and suffered from fleas") Sqealer manipulate them by saying " In those days they had been slaves and now they were free, and that made all the difference..."