Cloud computing represents a new computing approach that allows creating robust and on-demand services controlled by means of Service Level Agreements (SLA). These documents are generated following a process of negotiation during which the client chooses a subset of clauses among choices predefined by the provider on a "take it or leave it" basis. However, the heterogeneity between client requests and provider offers may result in inappropriate SLA. In addition, the cloud service context may change over the time which causes a client requirements adjustment and therefore, the SLA remains unsatisfactory. In this paper, we propose a cloud SLA negotiation and re-negotiation approach that integrate a semantic mapping between client requests and provider offers with the aim of generating a suitable SLA document. Moreover, our approach includes a context-aware system to adapt the SLA throughout reasoning techniques and automatically ensure the re-negotiation. A prototype implementation demonstrates the feasibility and the efficiency of our approach