Like FutureDoc said, if withdraw early enough it wont hurt your GPA. You need to check with your schools withdrawal policy for the dates. Usually if they let you withdraw with a Y for a grade its a no harm no foul thing. But it its late enough if the semester they may stick you with a W which is a withdraw with failing which has the same effect as an F on your GPA. An academic advisor at your school should be able to fill you in on the details for your specific institution.