Yes, you can reset full practice exams (which will also reset your scores for those tests). You can find a Reset this exam button at the bottom of the page for the specific practice section you want to reset.
A warning message will appear noting that this action will erase your progress in the whole exam (not just one section) and that it cannot be undone. If you would still like to reset the exam and your score, click OK.
Any progress in the practice exam and score for the exam will be erased.
Note: Resetting a practice exam won't return your skill level to the level it was prior to taking the Practice exam.
For more information, check out this article: What if I have to leave before the time is up?