You have to manipulate the PreferenceManager of the SettingsFragment. This is what it looks like
// Constants
//--------------------------------------------------------------------------
private final static String TAG = SettingsFragment.class.getName();
public final static String SETTINGS_SHARED_PREFERENCES_FILE_NAME = TAG + ".SETTINGS_SHARED_PREFERENCES_FILE_NAME";
// Life-cycle
//--------------------------------------------------------------------------
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Log.d(TAG, "onCreate()");
    // Define the settings file to use by this settings fragment
    getPreferenceManager().setSharedPreferencesName(SETTINGS_SHARED_PREFERENCES_FILE_NAME);
    // Load the preferences from an XML resource
    addPreferencesFromResource(R.xml.preferences);
}
Then you can access this settings file outside of the fragment like this:
SharedPreferences preferences = getActivity().getSharedPreferences(
        SettingsFragment.SETTINGS_SHARED_PREFERENCES_FILE_NAME,
        Context.MODE_PRIVATE);