Model Driven Software Engineering has matured over the last few years and is now becoming an established technology. As a consequence dealing with evolving metamodels and the necessary co-evolution of instances of this metamodel is becoming increasingly important. Several approaches have been proposed to solve model co-evolution problem. In this paper, Firstly, existing approaches in this area are analyzed to define requirements of our approach, namely automaticity, reuse, expressiveness and intelligence. After that we present a new approach CBRMig towards a solution to metamodel and model co-evolution problem. The core of our proposal is using a case based reasoning system that automates the process of creation and selection of cases to assist with the generation of a migration algorithm used for adapting models in response to metamodel evolution.