If the old one can read clearly, there is no point of uploading a new one. Unless there is content change. In addition, Mycic system has limit on file size so a high res file may be too large to upload.
Anyway, if you want to update a submitted document, the only way to do it is through CSE https://secure.cic.gc.ca/enquiries-renseignements/canada-case-cas-eng.aspx