Can I exchange a gift of diapers size one for a bigger size?

If it is a gift, you might not be able to. Still doesn't hurt to try. You may end up with store credit you can use for the right size

Yes, you can exchange even if you don't have a membership. You have to know who it was that gave it to you so they can look it up. You will receive store credit, which you can use in the store even if you don't have a membership. You can also go to the food court without membership anytime even if you're not using store credit.

That's all I want! Thanks