There are several ways. Here are some in the order of my personal preference:
1) Inject the another managed bean as a property of the one managed bean and just use it.
Here is an example.
2) Obtain the another managed bean by FacesContext and set it as a property.
Here are some ways.
3) Pass it through the session map which you obtain using ExternalContext#getSessionMap(). Let the one bean put the desired value in it and let the other bean get it.
Here is an example.