Can I change screenshots of the app after published?

Steps to update Screenshots on Android Developer Console

1. Select the App to which the screenshot to be added from the list of App

2. From the Left click on Store preference, and inside that select Store listing.
   
3. Scroll down on that page and you can see Graphic Assets, from there you can add

You can change the screenshots if you go to the Google Developer Console.

You select your app from the list, then go to store presence and select store listing from the menu on the left and there will be a graphic assets section on the page. You can add them there.