What should I do if I have uploaded a wrong submission by mistake. Can this be deleted from the harvard's server? Or should I just leave it and upload the correct one?
Just re-upload. You can upload as many times as you like until the cut-off date. Each time you upload the entire assignment is re-checked, so take care to include all the files on each upload, not just the ones that have changed. Also, remember to check50 before submitting.