Our paper deals with the update of component-based software architectures, i.e. all the modifications which can be performed on the architecture's elements to satisfy various requirements. Current researches on the component-based software engineering propose various mechanisms to adapt, evolve, customize, or reconfigure such architectures. We are convince that these mechanisms, even powerful, still require the architects' expertises. Moreover, it is noticed that these expertises conform to a style, i.e. a way of update which privileges certain concerns rather than others. It is what explains why a solution is selected instead of another, for the same main update issue. Our goal is to define updating styles, to represent and reuse update expertises. We wish to use this work to build an environment based on an updating style library in order to assist architects in modifying their component-based architectures.