Changing Prefabs Mid-Game

Ok, I am pretty new to Unity and C#. Because I am new I go check out the Asset Store. I downloaded a basic motion asset that has idle, running, jumping etc... models. But there are all prefabs. Now that I am done coding how my character moves, I want to be able change the prefabs so when my character is moving, he changes into the running prefab. How can I do this?

 

The prefabs are probably only examples. The animations themselves are in fbx files.