To provide their functionality, mobile apps interact extensively with the application programming interface (API) of the underlying operating system. Given that the API frequently evolves to incorporate crucial improvements, app developers are periodically required to update API usages in their apps to ensure that the apps behave as expected when running on the new API. To help developers with this tedious, error-prone, and time-consuming task, we defined a technique for automated API migration and implemented it in a tool called APIMigrator that supports Android apps. APIMigrator (1) automatically migrates API usages within an app by leveraging how developers of other apps migrated corresponding API usages and (2) validates the migrations through differential testing. We evaluated APIMigrator on a benchmark of 15 real-world apps and obtained promising results. Overall, our tool was able to migrate 85% of the API usages considered and validated 68% of these migrations. We provide a demo video of the tool at https://youtu.be/v0VfpKi_IDc.