You do not touch an unofficial transcript. The fact that it is unofficial does NOT give you license to alter it in any way. Any time you are asked for an unofficial transcript, it is because the people reviewing your application don't want to have to wait for you to be able to deliver an official transcript by certified mail; they are saying that it is acceptable to send a copy of what appears on your school's registrar's website.
If you have something bad on that transcript, it sucks, but it is not going to prevent you from doing anything; it is just another thing to explain. If you alter your transcript, however, that is, without question, grounds for eliminating you from consideration during the application process and for terminating you once you are accepted by the employer/scholarship/school.
Your best bet is to ignore it during your application but have a rock solid (and truthful) explanation prepared for your interview.