When you ask how it changed in the post-WWII years, how long are you talking about? How far does "post-WWII" extend? I'm going to answer this as if it only extends into the mid 1950s.
To me, the biggest change in popular culture during that time was the rise of a teen culture. During this time, teens came to have more leisure time and more disposable income than had ever been the case before. This helped lead to the growth of such things as rock and roll music.
So I would say that a major change in popular culture was a move towards music and other things that were popular with teens.