You may request to have your work regraded, but when you do so, you are submitting it for a complete regrade. Your score can go down as a result. For example, you might get back a point on an assignment that shouldn't have been taken off but you might lose other points that should have been taken off. Or you might get points back on one exam question only to find that you should have lost points on some other exam question.
Homework and exams are graded differently and so regrade requests are handled differently for each:
Students are encouraged to first discuss homework grading with their individual TA. If you aren't sure why you lost a point or if you disagree with the TA's evaluation, you should start by talking to your TA to see if you can resolve it directly. If not, you can request a regrade.