Obtain a blank DS-82 passport renewal form. These forms can be picked up from a local post office, or from the U.S. state travel website. A link to the form is provided at the Travel.State.Gov website.
Complete the form, which consists of your name, address, phone number, passport number (found on your current passport) and your signature. If you need to change your name or address for your passport, this is also the form to be used.
Take the completed form, as well as your current passport, to the local post office.
Have the post office take your passport picture. The post office will know all the photo regulations, such as a solid white background, your face being in the middle of the image with room around the boarders, no hats or other head clothing (some religious clothing will be considered as long as it doesn't cover the face) and no smiling. Also, pictures must not be blurry or have camera glares or red eye.
As of September 2009, it will cost you $75 to update your passport. Payments, such as a check, are made to the "Department of State." You can also pay with cash, debit or credit cards.
Give the photograph, the completed form, your current passport and payment to the postal worker at the post office and he will take care of it for you. You should receive your updated passport in the mail within a few weeks. The official will most likely look over your application just to make sure you didn't miss any important information. They will then send out the information to the U.S. State Department who will be in charge of granting your updated passport.