The main ways in which values having changed in the US in the past twenty years are the decline in the perceived worth of the traditional family, the increased focus on financial success, and the decrease in the profession of religious faith. Let's take a brief look at each of these.
The family, or what is defined as a family, has changed significantly. The nuclear family of a mother, father, and children is much less common today than it was only a few years ago. Single-parent families and same-sex parenting have increased over time, and many people no longer perceive a difference between various types of household units.
Further, there has been an increase in the focus on financial success and the acquisition of wealth. People spend many more hours working and have less leisure time than they did only a couple decades ago. Values have shifted from spending time in building relationships or in self-improvement activities to making more money and building one's career.
Finally, studies have shown that fewer people today profess any type of religious faith. Further, even if they profess a belief in God, people are less likely to practice that faith or make it a guiding force in their lives.
These observations reflect only general trends, of course, yet values certainly are changing in the United States as the years go by.