In a component-based software system, components are black boxes communicating through their interfaces, possibly using adapters. Whenever the requirements or the environment changes, the component-based software system must be adapted accordingly. We present a method that supports a systematic evolution of component-based software at the architectural level. It is based on operators and modification schemata that help to identify different architectural alternatives able to realize the evolution task. Furthermore, the method provides decision support in the form of heuristics to choose among the determined alternatives.