Systems need to be updated to last for a long time in a dynamic environment, and to cope with changing requirements. It is important for updates to preserve the desirable properties of the system under update, while possibly enforcing new ones. Here we consider a simple yet general update mechanism, which replaces a component of the system with a new one. The context, i.e., the rest of the system, remains unchanged. We define contexts and components as Constraint Automata interacting via either asynchronous or synchronous communication, and we express properties using Constraint Automata too. Then we build most general updates which preserve specific properties, considering both a single property and all the properties satisfied by the original system, in a given context or in all possible contexts.