The actions of any society or large group are determined by the moral and habitual values (culture) of the individuals in that group. If we wish to alter the behaviour of a group, we must alter the behaviour of the individuals.1)
People often talk about 'changing society', or 'changing the system', but society and the system are nothing more than the collective effects of individual behaviour. As such, society and the system can only be observed, not changed.
Fortunately, changing the behaviour of large numbers of individuals is not as mammoth a task as it appears. In fact, usually only a small minority (up to 10%) need to be sufficiently persuaded in order to influence the whole group. This is due to our innately social cohesive nature. 2)
We are given to being influenced by trends, thought leaders and each other. By and large we like to copy each other as it reinforces our status as part of the wider community. This is how we see widespread adoption of fashion, music or toy trends - through the virality of social forces.
An example of changing society
A good example of changing society through individual behaviour in recent years has been the advent of recycling. Over the last 20-30 years, governments, media and scientists all joined forces to back a massive campaign to change people's habits towards separating their trash for recycling purposes. This example is especially significant since there was no visible personal benefit to individuals.
Also, more generally, advertising, propaganda, viral videos, hashtag campaigns are all forms of shaping individual behaviour through coordinated external means. As has often been said, “if advertising didn't work, companies wouldn't pay millions for it”.