Constellations do change. The stars that make up constellations are independent, they have no way of connecting, so the constellation could change shape. So, just how fast do these constellations move and change? Well, stars travel very fast, but when they are far away from Earth, you don't notice these changes very often. Even though you don't think constellations don't change, trust me, they do.
Here are some examples of constellations changing overtime. The first one is what they DID look like, the second is what they look like now, and the third and the fourth are what they will look like.
Here are some examples of constellations changing overtime. The first one is what they DID look like, the second is what they look like now, and the third and the fourth are what they will look like.