It should reload in the simulator automatically. Any changes (e.g. saving) to files in the directory will trigger a reload.
However, I just updated my Android Studio on Windows to the latest version. Automatic reloading doesn’t work anymore. (But it works on my Mac.)
But I think it’s no big deal. I just close the app (clicking on the Overview button in simulator and swipe the app) in the simulator and press
a (for Android) in my command prompt.