Let's say you uploaded a student's submission, but want to replace it with a newer version. You can delete a student's submission directly from the Admin Console in a few clicks. 

To do, so navigate to the Submissions / By Student page and search for the student whose submission you want to delete. Once you've found him or her, click the "zoom in" button in the left-most column. Doing so will pull up a list of the student's submissions, by assignment.

To delete a submission, click the actions menu on the right side of the row corresponding to the submission you want to delete. Then select "delete submission." codePost will alert you if any other students are associated with this submission (as partners).