title: Update system app in android
body: <p>I have developed an android app and put this as prebuilt APK in AOSP.
  So the app will be installed in /system/app as a system app.</p>
  
  <p>The app has update function itself by downloading and installing the newer version APK.</p>
  
  <p>But it does not work because system app cannot be updated.
  Is there any way to update self-made system app?</p>