Sometimes people sign up for Facebook or Twitter accounts, but then decide for whatever reason that they want to permanently delete their account. Deleting your accounts (and all of the posts and pictures contained in them) can be a tedious process. Facebook has instructions for doing this here. And Twitter provides help with deleting your account here. If you don’t want to delete your entire account, but just delete some postings and better manage your content, TweetDelete can do that for your tweets and Facebook can help you manage your content with their Use Activity Log.
For more information on deleting content (or your entire account), check out the great article Swear Off Social Media, For Good or Just for Now, by Molly Wood in The New York Times.