Identify the reason you want or need to leave. Is the program not the right fit? Do you want to study something else? Do you have a personal situation or family crisis that requires you to put your studies on hold? Take the necessary time to think this through.
Decide if this is what you really want to do. You have to be clear and certain about making this move before you can explain your reasons to the necessary personnel in your program.
Fill out any necessary school forms. If you are leaving for good, you may not need to submit any. However, most schools do have a form for a leave of absence, where the student may return at a later date. Check your school's graduate catalog or bulletin for the proper protocol on how to submit this paperwork.
Make an appointment with your program adviser. Sit down with him and briefly inform him of your decision. Give a few reasons why, but be succinct in your explanation. If you have a good, trusting relationship with him, you can go into further detail. Have him sign any necessary school forms. Thank him for serving as your adviser.
Write a formal letter to the chair of your department indicating your decision to leave. You can simply state that you have arrived at this conclusion after careful deliberation and with the support of your adviser. You do not have to go into much more detail than this. Even if you are leaving due to a mismatch with the program, do not badmouth it in any way. Have her sign any necessary school forms.
Make an appointment to meet with the chair of the department. Give her the letter you've written, and briefly say that you wanted to tell her in person in addition to submitting a formal notice. Be gracious and leave the lines of communication open for potential future contact.
Send an email to your cohort and other classmates, if desired. You don't have to go into great detail with them about why you're leaving. Wish them well, and leave your contact information for potential future networking.
Submit any necessary forms to the proper personnel in your program and the university at large.