Error with sqlite database on android

I have this code to manage an sqlite database on android:

public class ConfiguracionSQLite extends SQLiteOpenHelper {

    public ConfiguracionSQLite(Context context) {
        super(context, "configuracion", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE configuracion (id_configuracion INTEGER, contenido TEXT)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    public void inicializarTabla() {
        SQLiteDatabase db = getWritableDatabase();
        db.execSQL("INSERT INTO configuracion (id_configuracion) VALUES(1)");
        db.close();
    }

    public Vector<String> comprobarTabla() {
            Vector<String> result = new Vector<>();
            SQLiteDatabase db = getReadableDatabase();
            Cursor cursor = db.rawQuery("SELECT * FROM configuracion", null);
            while (cursor.moveToNext()) {
                result.add(cursor.getString(0));//id_configuracion
                result.add(cursor.getString(1));//contenido
            }
            cursor.close();
            db.close();
            return result;
    }
}

So far so good. The problem comes when I add one more field to the table:

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL("CREATE TABLE configuracion (id_configuracion INTEGER, contenido TEXT, contenido_2 TEXT)");
}

public Vector<String> comprobarTabla() {
        Vector<String> result = new Vector<>();
        SQLiteDatabase db = getReadableDatabase();
        Cursor cursor = db.rawQuery("SELECT * FROM configuracion", null);
        while (cursor.moveToNext()) {
            result.add(cursor.getString(0));//id_configuracion
            result.add(cursor.getString(1));//contenido
            result.add(cursor.getString(2));//contenido_2
        }
        cursor.close();
        db.close();
        return result;
}

If I uninstall the application and reinstall it, there is no problem, but if what I do is an update, then I have an error here: result.add(cursor.getString(2));//contenido_2

How can I update the sqlite database when I update?

This is the error log:

  

java.lang.IllegalStateException: Could not read row 1, col 2 from   CursorWindow. Make sure the Cursor is initialized correctly before   accessing data from it.