Q: Can I upgrade storage on my iphone?

No, you cannot. Storage on the iPhone is fixed. The only way to increase storage on an iPhone is to purchase a larger capacity one.

Apple does not really have a trade-in program, they do offer a recycle service. The amount you receive is generally not that high, so not so many people take advantage of it. You can sell it outright yourself, or can also look into other companies that purchase used electronics. Try this link to view the recycle program. https://www.apple.com/recycling/

You're welcome. Have a nice day.