Click on the old file and you will see an option to delete the old one. You can now enter an updated file.
Caution should be taken as you approach the date/time the project is due. Overwriting a file may cause it to be recorded as being submitted late and it will not be graded.
In some cases, an update may not be worth the risk.
DO NOT send me an e-mail attachment if you are late. You may lose up to 50 points from your course total if you try to skirt the regulations.