1 Log into iTunes Connect.
2 Click on "Manage Apps" and then the app you want to edit.
3 Click "View Details" on the version of your app.
4 Then click the "Edit" button next to Metadata and Uploads.
5 You can click the close button (x) to delete a screenshot, and click Choose File to upload a new one.6 After you have made the changes you want, make sure to click Save. Or click Cancel to exit without saving.
Refer to this documentation from Apple, Table 7-9 for requirements: