Android Apps are frequently updated, every couple of weeks, to keep up with changing user, hardware and business demands. Correctness of App updates is checked through extensive testing. Recent research has proposed tools for automated GUI event generation in Android Apps. These techniques, however, are not efficient at checking App updates as the generated GUI events do not prioritise updates, and instead explore other App behaviours. We address this need in this paper with CAT (Change-focused Android GUI Testing). For App updates, at the source code or GUI level, CAT performs change impact analysis to identify GUI elements affected by the update. CAT then generates GUI event sequences to interact with the affected GUI elements. Our empirical evaluations using 21 publicly available open source and 2 commercial Android Apps demonstrate that CAT is able to automatically identify GUI elements affected by App updates, generate and execute GUI event sequences focusing on change-affected GUI elements. Comparison with two popular GUI event generation tools, DroidBot and DroidMate, revealed that CAT was more effective at interacting with the change-affected GUI elements. Finally, CAT was able to detect previously unknown change-related bugs in two open source Apps. Developers of the commercial Apps found CAT was more effective than their in-house GUI testing tool in interacting with changed elements and faster at detecting seeded bugs.