You can apply
Online – use our Social Security Retirement Benefit Application.

By phone – call us at 1-800-772-1213. If you are deaf or hard of hearing, you can call us at TTY 1-800-325-0778.

In person – visit your local Social Security office. (Call first to make an appointment.)

If you do not live in the U.S. or one of its territories – contact the nearest U.S. Social Security office, U.S. Embassy or consulate, or the Veterans Affairs Regional Office (VARO) in the Philippines.

Reminders:

You must be at least 61 years and 9 months old to apply for retirement benefits.
You should apply for benefits no more than four months before the date you want your benefits to start.
If you are already age 62, you may be able to start your benefits in the month you apply.
If you are not getting Social Security and you are not ready to retire, you should still sign up for Medicare four months before your 65th birthday.
http://www.socialsecurity.gov/retire2/applying8.htm