To edit receipts, they need to be unlocked if they have been published and not be approved.
To unlock the recepit you would go to Suppliers > find the receipt you want to edit > Click the icon on the right which says, “Unlock" and click this.
To remove their approved state, you would go to Suppliers > find the receipt you want to edit > Click the icon on the right which says, “Withdraw Approval” and click this.
You will then see a row of icons on the right hand side of the receipt, click the one which has the pencil icon. From there you can edit the recepit. Once the edits have been completed click "Save and Exit".