Business process optimisation is a strategic activity in organisations because of its potential to increase profit margins and reduce operational costs. In this paper, we focus on a specific technique used for process optimisation known as process refactoring. In this work, a process is described using BPMN extended with quantitative aspects for modelling execution times and resources associated with tasks. A process is not executed once but multiple times, and multiple concurrent executions of a process compete for using the shared resources. In this context, we propose a refactoring approach whose goal is to reduce the total execution time of the process and optimise the usage of the shared resources. To do so, we first analyse the given process in terms of task dependency and resource usage, and then rely on these results to restructure the process and return an optimal version of it. This process refactoring technique is fully automated by a tool that we implemented and applied on several examples for validation purposes.