How can I return my iPhone 15 Plus with a cracked screen and upgrade to iPhone 15 Pro Max?

No. You can’t. Even if it were in perfect condition, Apple doesn’t take the iphone 15, pro, or pro max in trade at all right now.

You can pay to get it fixed or replaced with the exact same model if the damage is more substantial than just the screen.

Hello,

You could trade it in, but you would get a reduced price due to the cracked screen. See this:

Turn the device you have into the one you want

Good luck.

I don’t know if Apple is accepting any iPhone 15 series phones for trade-in yet. If they are, a broken screen would definitely reduce trade-in value.