Can I exchange my iPhone 7 with 32gb with an iPhone with more storage

You could sell it and buy whatever you like.

Some carriers offer trade programs, you could ask your.

Apple offers one as well:

iPhone Trade-up - Apple

For phones purchased directly from Apple, if you're within the 14 day purchase window, you can return the 32gb phone and the select one with more storage.

However, if you have had it for longer than that, your best bet would be to sell it privately and then purchase another phone.