Replacing uploaded files in IRIS

I want to replace the current reference zip folder in my ODD submission (needed as additional references used in response to validation) with an updated reference zip folder, but am unable to a, delete the original zip folder or b, overwrite the original zip folder. Is there a way  of replacing the original that I am missing or do I just upload an "updated" Bibliography zip folder in addition to the original.

In principle it should be possible to overwrite an existing uploaded file in an IRIS submission, simply by re-uploading a file with the exact same name and extension. Of course, to do that the submission must have been (temporarily) reopened by EMA staff: submissions are normally locked during the evaluation process. If reuploading with the same name fails for any reason, it is always possible to upload an updated version of the same file, with a suitable name, but this should not be needed.

Thank you for your response, I had thought it might have been to do with it being a folder. But we will reach to our contact in the first instance to ensure the submission has been (temporarily) reopened, just in case that might be the issue. Thanks again for the alternatives to try