I just bought Iphone 13 pro recently and i realized i want iphone the pro max

It depends on when and where you bought it. See the 'U.S. Returns & Refunds Policy' in:

Returns & Refunds - Shopping Help - Apple

If you purchased your iPhone 13 pro in the USA after November 01st and before December 25th, 2021, then your return period ends on January 08th 2022. If you purchased your iPhone before November 01st, 2021 then the standard return policy applies and that is a 14 day period.

Axel F.