Drag/Drop or browse and add the screenshots that you want converted to the correct size for the app store.
For best results ensure the screenshots were taken from a phone or simulator that is the same as the output phone type.
The AppStore needs screenshots in a specific resolution. If screenshots taken from a phone or simulator does not match the resolution needed AppStore will not accept them
This online tool will fix any uploaded screenshots to be compatible with the AppStore. You can then download a zip of the fixed screenshots that can be uploaded to the AppStore.
Select the phone used to capture the screenshots: