swap my iphone

If it’s within 14 days, you can return for a refund, and re-purchase.

If it’s outside 14 days, you’ll be doing a trade-in. Or selling privately.

As the previous reply correctly stated, this is all covered at the Apple web site.

Here are the results for the associated web searches:

Returns & Refunds - Shopping Help - Apple

Apple Trade In - Apple

What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

Check Apple's web pages for details.