Software architecture is the abstraction of a software system, that significantly influences software development and maintenance. As software evolves, continuous changes could deviate its architecture from the original design, leading to architecture degradation that causes a decline in software quality. Architecture refactoring becomes necessary to address or mitigate architecture degradation for improving overall quality. Although researchers have developed various architecture refactoring tools and techniques, there has been limited research on how architecture refactoring is practiced in real-world scenarios. In this paper, we conducted an empirical study by analyzing posts from Stack Overflow to understand architecture refactoring in practice. Through our analysis of 694 posts with 3,468 discussion threads, we identified 12 types of architecture refactoring based on two classification dimensions. Additionally, we categorized architecture problems faced by practitioners and explored their corresponding refactoring solutions. Furthermore, we revealed six potential risks that may result from architecture refactoring. We believe that our study can provide valuable insights for practitioners to perform architecture refactoring effectively. The findings can serve as a foundation for future research and offer practical guidance to improve architecture quality.