QB Issue Resolution:

You will just need to click “X” sign. That’s to delete. And, if you want to attach new one (click paper click icon for new attachment), you can do so as well. See attached screenshot photo for reference.

Resolution for Issue 'After attaching a document to an invoice, if there is a change, how do I delete the attachment?' available: Yes (Solved).
Source: Intuit Community forum.

After attaching a document to an invoice, if there is a change, how do I delete the attachment?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for Invoice
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Error Recovery for Invoice [Canada]
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