Right now there's no option to switch the size/color/version — you'll need to cancel the original order and repurchase the item.
Here's how:
On the website:
- Go to My orders.
- Select the order from the list.
- Select Cancel order.
- Select the cancellation reason, then – Confirm.
On Android:
- Go to Profile by tapping the icon in the bottom right corner.
- Select My orders.
- Select the order from the list.
- Select Cancel order.
- Select the cancellation reason, then – Confirm.
On iOS:
- Go to Profile by tapping the icon in the bottom right corner.
- Select My orders.
- Select the order from the list.
- Select Cancel order, then tap Yes.
N.B. You have only two hours to do it, while the order still has the Paid status.