You can edit the metadata (images and texts) of your app via the iTunesConnect.
1. Log into iTunesConnect at https://itunesconnect.apple.com
2. Click on Manage Your Apps
3. You will see a list of all your apps. Click on the app you wish to edit.
4. In the screen that opens, you will see the current store version.
5. As you scroll down, you will see all the metadata and you will be able to change some of it. You can click on the question mark signs to learn more about a specific field.
6. Once all the data has been entered, scroll up and click on 'Save'.