Return/exchange policy

Hi, one week ago I bought 2 iPhone XS at www.apple.com. Both phones were delivered to a US location but now I'm in Spain. I'm happy with my phone, but my wife (it was a present for her) would like the XS Max instead of the XS. Is any of the follwing options viable?

Option 1. In around 20 days, a colleage of mine is going to the US. Could she fly back to the US with the phone (it is still packaged, the box has not been opened) and return it or change it there? (paying the difference in the case of a change, of course)

Option 2. Can I return it in any of the Apple Store located at Madrid?

Option 3. Can I change it for an XS Max in any of the Apple Store located at Madrid? Paying the difference between both phones, of course.

Thanks in advance for your support, Rafa