The environment of businesses is naturally unstable and dynamic due to increasing market constraints and events. Thus business processes are frequently subject to changes which must be supported by process models and systems that implement them. This paper deals with adaptation of IOWF (Inter-Organizational Workflow) process models based on services. It states conceptually, the most frequent adaptations that can be operated on IOWF models described through the concept of orchestration function which abstracts the control flow of the process. Thus, operations of adaptation turn to modification of services and transformation of the orchestration function describing the model. We particularly distinguish evolutive adaptation leading to expansion of the cooperation and/or the global functionality of the process.