In this paper, we present a network management framework based on OpenFlow technology, to enhance flexibility in network management to conform more service requirements from diverse user identities. To this aim, user-level based QoS differentiation is introduced to provide fine-grained handling of network flows under different user and service constraints. With user identity and service requirement in place, we are able to provide dynamic bandwidth adjustment with the support of traffic statistics and even allocate and share unutilized network resources to satisfy user service requirement and improve resource utilization in networks. Furthermore, we also present a unified but simple network management interface to help network administrators to manage a network as a single entity. With this interface, the agents in switches are developed to detect and response to anomalies of flows. In summary, the proposed framework improves the original OpenFlow framework to provide a flexible and agile way to manage networks with dynamic resource allocation and to meet the diverse QoS requirements in future cloud services.