The post war era was the popularization of Rhythm and Blues music which led to Rock and Roll music. This period also saw the world of professional sports expand from the east coast to the west. Movies and movie stars became more easily accessible with the inventions of television.

As the economy grew, so did the demand for consumer goods.  Life got easier with advancements in modern conveniences and automated machinery.  Installment plans enabled people to get these appliances and conveniences (electric washers and dryers, televisions, etc.) into their homes like never before.  Transportation and communication got cheaper and more efficient, allowing more travel than ever before--as well as an increase in the need for gasoline and the advent of motels (motor hotels) for those on the road.  Having free time to spend on a variety of pursuits was the major cause of all the pop culture elements of the late '40s and especially the '50s.

The culture changed with economic prosperity, just as it did in the 1920s.  With leisure time, modern conveniences, material goods, their own homes and decent wages, people were more able to concentrate on art, music, sports, vacations and materialism, which has been the outline of our culture since that time.

There were many changes in popular culture following WWII.  First, television began to become more widespread throughout the United States. This led to huge changes in pop culture with the emergence of TV stars such as Milton Berle, Lucille Ball, and James Arness, along with the creation of popular TV shows such as the Tonight Show.  Another change occurred when professional sports moved to the west coast and became integrated creating such stars as LA Dodger Jackie Robinson.  These are just some of the changes that occurred after WWII that changed pop culture in the U.S.

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.