If you have added the wrong receipt to a payment, don't panic.
First, you need to add the right receipt to be able to delete the previous one.
Here's how to replace a receipt:
Delete a receipt on a Payment
Go to the "Payments" tab.
Select your payment or that of the collaborator.
Click on "Upload another receipt" or drag-and-drop the receipt on the right sidebar.
Click on the incorrect receipt.
Click on the "trash can" tool at the top left of the pop-up window that appears with your receipt.
It looks like this (see top-left corner):
That's it!
Delete a receipt on an Expense claim (after payment)
Your collaborator added too many receipts and you want to delete one of them?
Wait till it's marked as paid.
Go to the "Payments" tab.
Select your payment or that of the collaborator.
Select the receipt to delete
Click on the bin icon (as above)