As ConfTool Admin and/or Chair you have access to those files and can also edit or delete them.
Please go to:
Overview => Submissions & Reviews => List of Submissions … and in the column "Reviewers / Reviews" click on "Reviews" (image 1).
On the following page "Contribution Details" choose the review you want to access by clicking on the title "Review X" (image 2).
Now you get to a page that shows the review details. At the bottom of the page select the option "Update Uploaded File for Author" (image 3).
On the new page you can either upload a new file or delete the current upload (image 4).
If you need information on editing reviews as well, please consult this
page.
Information on file uploading by reviewers is available
here.