Wal-Mart, Sam's Club and Veterans of Foreign Wars offer flag disposal services. Find locations using the locator tools on their respective websites, as of 2015. The U.S. Flag Code specifies burning as the preferred disposal method for flags.
To find a Wal-Mart in your area, visit the Walmart.com home page and click Store Finder. SamsClub.com has a Club Locator link, while the VFW.org link says Find A Post.
To dispose of the flag yourself, fold it in its customary manner. Start a fire, and use enough material to burn the flag completely. Set the flag into the fire. Once the flag is gone, put out the fire, and bury the ashes. Follow any fire laws in your area.
To show respect for the flag so it has a dignified disposal, stay silent, say the Pledge of Allegiance, or salute while the flag burns. A short flag-burning ceremony is also appropriate.
Another way to dispose of the flag yourself is to cut it in half vertically, and then place the halves on top of each other and cut them in half horizontally. Avoid cutting any of the blue star field. After it's cut, it's not technically a flag anymore, so you can place the pieces in a container and dispose of it.