Complete guide : https://developer.android.com/studio/build/application-id.html
As per Android official Blogs : https://android-developers.googleblog.com/2011/06/things-that-cannot-change.html
We can say that:
If the manifest package name has changed, the new application will be installed alongside the old application, so they both co-exist on the user’s device at the same time.
If the signing certificate changes, trying to install the new application on to the device will fail until the old version is uninstalled.
As per Google App Update check list : https://support.google.com/googleplay/android-developer/answer/113476?hl=en
Update your apps
Prepare your APK
When you're ready to make changes to your APK, make sure to update your app’s version code as well so that existing users will receive your update.
Use the following checklist to make sure your new APK is ready to update your existing users:
To verify that your APK is using the same certification as the previous version, you can run the following command on both APKs and compare the results:
$ jarsigner -verify -verbose -certs my_application.apk
If the results are identical, you’re using the same key and are ready to continue. If the results are different, you will need to re-sign the APK with the correct key.
Learn more about signing your applications
Upload your APK Once your APK is ready, you can create a new release.