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
6. In the same section, you can edit the Store listing (short and long description, phone number, website) and SAVE it.
Hope this helps!
Want us to do this for you ? Mail us at firstname.lastname@example.org, we'd be happy to assist you :)