How to accommodate iphone and ipad backgrounds (minus scaling)

So I have an app made but the scaling is not amazing on iPhone and iPad (background looks wide so it's out of proportion).

Is there a way to call an image depending on device?

e.g. adding -ipad.png to the description?

Check this out by clicking on 'ipad' or 'iphone' to see what I mean:
https://itunes.apple.com/gb/app/ten-second-game/id1033677910?mt=8

Thank you