In regression GUI testing for Android apps, test scripts often fail due to changes to, rather than faults in, those apps. To avoid such false positives while still retaining the value of the old test scripts as much as possible, programmers need an automatic way to maintain the tests after the corresponding GUI has evolved. In this paper, we propose the CHATEM approach to automate GUI test script maintenance for Android apps. Taking as input the models for the GUIs of the base and updated version app and the original test scripts, CHATEM automatically extracts the changes between the two GUIs and generates maintenance actions for each change, which are then combined to form the maintenance actions for affected test scripts. In an experimental evaluation on 16 Android apps, CHATEM was able to automatically maintain the test scripts so that overall more than 95% of the remaining behaviors tested before are still tested, and almost 80% of the reusable test actions are retained in the result tests.