Handling of obsolete software and/or hardware components together with management of function updates in a complex embedded system with an expected life time of more than 30 years can be a very difficult to almost impossible task. This types of challenges can be found in a large number of companies in, for example, the power transmission industry, power plants, aviation etc. In this paper we present the basic steps in a proposed method for handling evolvability in such embedded systems with long expected life cycles. The key elements of the proposed method are the definition of function dependencies, release planning, and test requirements.