Tap any listing in My Listings to update it — the form pre-fills with what you already entered. Your changes go live straight away, whatever you change, and the listing never comes off Browse while you edit it.
One thing worth knowing: rewriting a listing heavily after it's been up — swapping the item, or moving the price a long way — is something our team looks at more closely, because it's what a bait-and-switch looks like. An honest correction is fine.