E-commerce applications are designed to streamline the business processes for an organization. Graphical user interfaces allow business users to perform daily business activities by interacting with ecommerce applications through menu-driven user interface components, such as toolbars and dialog windows. However, business users are often overwhelmed by the enormous functionality available. Users struggle in deciding where to start and where to go next in order to accomplish tasks required by business processes. In this paper, we utilize the knowledge embedded in business processes to reengineer the user interfaces of existing e-commerce applications that implement business processes. We aim to improve the usability of user interfaces by providing contextual information and guiding users to fulfill business processes step by step. We evaluate our proposed approach by reengineering the user interface of an existing e-commerce application.