While your phone is powered off,

  1. Press and hold [Volume Up], [Home], and [Power] buttons together.
  2. Release them when the Galaxy S boot up animation is shown.
  3. Select "wipe data/factory reset" to hard rest. Use the [Volume Up], [Volume Down] to navigate through the list, and [Home] to select.
  4. Lastly, select "Yes -- delete all user data" to confirm the hard reset