If you feel that there was an error in grading your homework or exam, then you need to write on a piece of paper a description of the error. STAPLE the paper to your homework or exam and leave it with me to be regraded.
I start marking with a list of expectations for each homework assignment and exam problem and a scheme for where to take off points. So if your complaint is that too many points were taken off for one kind of mistake or another in your homework, then generally those types of things will not change in a regrade.
If there is a genuine error in the marking, like I thought something was missing, but it is really there, then you will likely get points restored.
HOWEVER, a regrade means that the entire assignment or exam will be remarked, so be aware that your mark can go down as well as up.
Regrades take while to process, so be patient. If you need the work to study from, then make a copy of it before you turn it in for a regrade.