Norms are the rules and standards of a group. A member's behaviour is dictated by the group's norms. Members learn about the norms from other members.
Shared values and beliefs influence the creation of the group's norm. These rules and standards determine which behaviours are deemed suitable, acceptable and desirable by group members.
Good behaviour will be praised. Bad behaviour will be punished.
For example, one group may say it's good behaviour to share food because you are considerate. Another group may say it's bad behaviour to share food because it may spread germs or diseases.
Norms are created by people within the group. For norms to change, the people must change. For people to change, they can either leave the group and recruit new members.
Or people themselves learn, gain experience and adopt different values, beliefs and mindsets. With this new mindset, you can new norms by praising desirable behaviour and punishing undesirable behaviour.
You have the power to create new norms. When you want social norms to change, you need to change.