What if the item I want costs more or less than the one I'm returning?Updated 3 days ago

Either way, you're covered:

Costs more? Pay the difference on the portal, where a payment window will open for you to enter your card details. This amount is charged at the time you place your exchange, not held as an authorisation. From there, choose how you'd like to receive your new item:
Instant Exchange — your new item ships straight away, and you'll follow the standard Instant Exchange process above (card authorisation hold, 28 days to return your original item).
Standard Exchange — you send your original item back first; once it's received and processed, we'll ship your replacement.

Costs less? You've got three options for the difference
Refund — the difference is refunded to your original payment method.
Store credit — choose store credit and it's sent to you as soon as your exchange is logged.
Put it toward something else — add another item to your basket and use the difference toward it, paying any remaining balance directly on the portal.