Turnitin assessments can be set to allow single or multiple submissions.
If multiple submissions are allowed, just upload the newest version of your assignment. Only the last document you upload will be marked. The one you want to delete will still show, but will not be assessed.
For single submission assignments, you cannot delete or replace the document. You will have to contact your lecturer directly if you have made a mistake.
A variety of Turnitin-related guides with step by step instructions are available on the webpage linked below.
