How to change the country on your iphone on app store?

My mum's partner shares the same apple ID as me. They went to New York and received a voucher, therefore their app store country changed from UK to USA. They spent most of their voucher but have $0.49 left and their isn't any apps costing $0.49.It won't let me download anything unless i change my country on it and i can't. Any suggestions?

It should be in your iPhone settings, not in the App Store.

Country should be in your setting in general. For you apple Account try going on iTunes and go into your apple I'd settings