After you log in and go to the particular protocol to edit in Protocol inbox, there will be a 'Request Edit' button for each Protocol opened. After you click on ‘Request Edit’ button for the Protocol. There are remove buttons next to each attachment, as highlighted in red box below. After clicking on these remove buttons, the attachments will be deleted from the protocol.
To upload new attachments in this page, select the form name that you are attaching from the drop down list. Then the 'Browse/Upload' button will be visible. Click on this button to select file to upload.