How do i delete a poor image of a receipt to then re enter correctly?

Thanks for visiting the Community, @stewart6. You can open the sales forms you've created, then go to the Attachment section and select the X next to the file name to remove it. 

Once done, re-take a photo of your receipt and ensure to preview it first to make sure you're attaching a clear copy this time. 

For your reference, check out this article: Attachments in QuickBooks Online. It helps you learn about the acceptable file type you can attach and what transactions that can keep attachments in Quickbooks. 

Let me know if you have additional concerns. We're always delighted to help.