Type up a description of why you feel your grade is currently incorrect. Staple this sheet to your exam and give it to me or drop it in my mail box. You should probably keep a Xerox copy since it might take a while for the regrade to happen.
The regrade will be based only on what you submit in writing, not what you might tell me in person. With some 100+ students, I am likely to say, "of course that makes sense" after class and then totally forget what you told me when I look at it a few hours later.
Regrades will only be discussed in office hours if no one needs help on material. Learning takes precedence over grading! You will still have to type up your issues before it will be regraded.
If there is an error in totalling up your score, you may write this on the cover of your exam. Say what you think the total should be.