Rapidly changing market conditions and IT systems are forcing companies to adapt their business processes more dynamically than in the past. Most current commercial BPMS products lack the full capability to support changing processes. To address this challenge, we discuss three aspects of dynamic adaptation in a BPM system: model-level, instance-level, and runtime environment changes. We focus on analyzing the patterns of the instance-level navigation changes, including the preconditions, actions and consequences of each change. Based on this analysis, we propose a system design for the runtime environment to support dynamic instance-level changes. We have implemented a prototype of such a system with the motivating scenarios to demonstrate the usefulness of our proposal.