Here's how you can change the app icon and screenshots on google developer account-
1. Log in to Google Developer Account
2. Select the App
3. Go to 'Store Presence' and select 'Store Listing'
4. Change the icon with the resolution 512 x 512 32 bit PNG (with alpha)
5. Go to Phone and select Browse files
Hope this helps!
Want us to do this for you ? Mail us at email@example.com, we'd be happy to assist you :)