An APK file is the file format used for installing software (usually games or apps) on the Android operating system.
APK files related to your App allow you to update the App without having to republish it.
To do so, follow these simple steps:
1. Download your APK file from your AppsBuilder dashboard
Click on Promote from the top bar:
Then click on Publish on Stores from the left hand sidebar:
Select Google Play from the list of publishing platforms:
And then on Download your APK file from the right hand list:
2. Upload the APK file for your App into your Google Play Developer Account dashboard
Log into your Google Play Developer Account and click on All Applications from the left hand sidebar:
Then click on APK from the list menu:
And finally click on the blue button to upload your new APK file: