The Scrum Guidance Body usually defines a process for approving and managing changes throughout the organization. In the absence of a formal process, it is recommended that small changes that do not have a significant impact on the project be directly approved by the Product Owner. The tolerance for such small changes could be defined at an organizational level or by the sponsor for a particular project. In most projects, 90% of Change Requests could be classified as small changes that should be approved by the Product Owner. So, the Product Owner plays a very important role in managing changes in a Scrum Project.
Reference: http://blog.scrumstudy.com/how-to-handle-request-for-change-or-change-requests-in-a-scrum- project-2/