The Seven Commandments, as set down by Old Major, are supposed to form the basis of the new Animalist utopia built by the animals after Mr. Jones is sent packing from the farm. But over time, Napoleon and the other pigs start making subtle changes to each Commandment, to provide cover for their many nefarious acts and to give them free reign to do as they please.

The First Commandment states that whatever goes on two legs—i.e. is a human—is an enemy. Yet Napoleon blatantly violates this Commandment by engaging in lucrative trade with the nearest town and with local farms.

The Second Commandment states that whatever goes upon four legs or has wings is a friend. But try telling that to the hens massacred on the orders of Napoleon for refusing to hand over their eggs. Some friendship this is!

The Third Commandment states that no animal shall wear clothes. Napoleon, however, fancies himself as a bit of a sharp dresser, so ends up disregarding the commandment entirely. The pigs like wearing clothes, which is one of the reasons why it becomes increasingly difficult to tell them apart from humans.

The Fourth Commandment is pretty emphatic that no animal shall sleep in a bed. Why? Because that's something that humans do, and humans are to be hated and despised. But this is yet another commandment that goes by the board as Napoleon rather likes sleeping on beds. So he subtly changes this Commandment to read "No animal shall sleep in a bed with sheets".

The Fifth Commandment, with its prohibition on animals drinking alcohol, is another one designed to prevent animals from behaving like humans. But once Napoleon discovers the contents of Mr. Jones' drinks cabinet, then it's time for another subtle change in Old Major's teachings. Now, the Commandment states that "No animal shall drink alcohol to excess". Yet even this is blatantly violated by Napoleon, who's such a greedy pig.

The Sixth Commandment is one of the most important: No animal shall kill any other animal. But it's also the one most honored in the breach than the observance. Once Napoleon establishes himself as dictator of the farm, he has no hesitation in killing any other animal who gets in his way.

Last, but not least, we have the Seventh Commandment: All animals are equal. In actual fact, however, some animals are more equal than others. While most of the animals work long hours in return for ever-diminishing rations, Napoleon and the pigs get to live like kings.

The pigs, being more intelligent than the other animals, seize control of Animal Farm after the rebellion and gradually, with the support of the dogs, transform it from an experiment in equality and plenty for all to one of hierarchy and privilege for themselves. The Seven Commandments were meant to protect the rights of all the animals, so the pigs have to change them in order to get away with commandeering most of the benefits of the farm for their own exclusive use. The Seven Commandments are as flollows:

1. "Whatever goes upon two legs is an enemy." The pigs break this when they enter into business dealings with humans. For example, they sell poor, devoted Boxer to the glue factory, owned by the humans, when he is old and worn-out at the end of the book. 
2. "Whatever goes upon four legs, or has wings, is a friend." Anyone who does not go along with Napoleon, even if an animal, is an enemy. For instance, Napoleon has the dogs kill the hens who refuse to give up their eggs to sell to the humans. He runs Snowball off the farm. 
3. "No animal shall wear clothes." The pigs wear clothing.
4. "No animal shall sleep in a bed." The pigs sleep in beds in Mr. Jones's farmhouse.
5. "No animal shall drink alcohol." This rule was a response to the neglect the animals endured due to Mr. Jones's drinking. The pigs, however, drink alcohol—and even get drunk.
6. "No animal shall kill any other animal." Napoleon, as in Stalin's Soviet Union, has trials and has executed animals deemed traitors.
7. "All animals are equal." By the end of the book, the pigs have become a separate caste, living well, walking on two legs, carrying whips, and wearing clothes. In contrast, the rest of the animals are just as poor and overworked as they were under Farmer Jones. All the animals are not equal, and the pigs deal with this problem by adding to this commandment. This commandment will eventually state, illogically, that some animals are more equal than others.

In Animal Farm, the Seven Commandments represent the animals' utopian dreams after they overthrow Mr Jones in Chapter Two. It does not take long, however, before the commandments are broken by the power-hungry and corrupt pigs. Here is a glimpse of how this happens:

1. "Whatever goes upon two legs is an enemy." This commandment is broken when Napoleon begins trading with the neighbouring humans, Mr Pilkington and Mr Frederick. In addition, by the closing scene of the novel, Napoleon has adopted human dress and walks around on his hind legs.
2. "Whatever goes upon four legs, or has wings, is a friend." Napoleon breaks this rule when he runs Snowball off the farm in Chapter Five and later portrays him as an enemy of Animal Farm. 
3. "No animal shall wear clothes." By the final chapter of the novel, all of the pigs can be seen in human clothing which they have taken from Mr Jones' wardrobe.
4. "No animal shall sleep in a bed." The pigs break this commandment in Chapter Six when they move into the farmhouse to be more comfortable.
5. "No animal shall drink alcohol." Napoleon changes this commandment to include the words "to excess" in Chapter Eight after he drinks whiskey for the first time and suffers from a terrible hangover.
6. "No animal shall kill any other animal." Napoleon breaks this commandment when he brutally slaughters the hens who rebel against him in Chapter Seven.  
7. "All animals are equal." This commandment is famously changed in the final chapter of the book when Napoleon declares that some animals are "more equal than others." This sums up the divide between the pigs, the ruling class, and the other animals on the farm.  

Although it is unintentional, the first major corruption of the Seven Commandments of Animalism comes when Snowball, with good intentions, creates a distilled law: "Four legs good, two legs bad." While it helps to instill the ideals of Animalism in all the animals, even those without much intellect, it starts the path of simplification that ends with the seven rules converted into one rule: "Four legs good, two legs better."

The first proper corruption of the Commandments comes when the pigs move into the farmhouse, sleeping in beds, directly against the original wording of the laws:

"...You did not suppose, surely, that there was ever a ruling against beds? ... The rule was against sheets, which are a human invention... You would not have us too tired to carry out our duties? Surely none of you wishes to see Jones back?"
(Orwell, Animal Farm, msxnet.org)

With this change, it becomes obvious to the pigs that they can slowly alter the rules and as long as Squealer appeals to their fear and hatred of Farmer Jones, the other animals will forget the original wording and believe the new wording. More changes follow, giving the pigs the ability to take on human attributes while keeping the other animals oppressed. This sets up the farm to change from a community of equality to a dictatorship, and all done with the implicit approval of the other animals, who cannot think far enough ahead to see what these changes will mean.