Android SQLite won't execute onUpgrade()

I'm trying to add some columns to my SQLite database. I keep having the following error:
no such column: n_livello (eg. the new column I'm adding)
and the app installation fails with timeout.
It seems that onUpgrade() method is never called.
This is my code:

public class DBHelper extends SQLiteOpenHelper {

   public static final String DATABASE_NAME = "geko";
   static final int DATABASE_VERSION = 2;

   public DBHelper(Context context){
      super(context, DATABASE_NAME , null, DATABASE_VERSION);
   }  

   @Override
   public void onCreate(SQLiteDatabase db) {

      String CREATE_FRA_TABLE = "CREATE TABLE IF NOT EXISTS "+ FRA_TABLE_NAME + " ("
              + FRA_COLUMN_ID + " INTEGER PRIMARY KEY, "
              + FRA_COLUMN_USERNAME + " TEXT, "
              + FRA_COLUMN_NUM_LIVELLO + "INTEGER, "
              + FRA_COLUMN_LIVELLO + " TEXT, "
              + FRA_COLUMN_TEMPO + " TEXT, "
              + FRA_COLUMN_DATA_PARTITA + " TEXT,"
              + FRA_COLUMN_INVIATO + " INTEGER)";

              db.execSQL(CREATE_FRA_TABLE);

      String CREATE_ING_TABLE = "CREATE TABLE IF NOT EXISTS "+ ING_TABLE_NAME + " ("
              + ING_COLUMN_ID + " INTEGER PRIMARY KEY, "
              + ING_COLUMN_USERNAME + " TEXT, "
              + ING_COLUMN_NUM_LIVELLO + "INTEGER, "
              + ING_COLUMN_LIVELLO + " TEXT, "
              + ING_COLUMN_TEMPO + " TEXT, "
              + ING_COLUMN_DATA_PARTITA + " TEXT,"
              + ING_COLUMN_INVIATO + " INTEGER)";

              db.execSQL(CREATE_ING_TABLE);
   }

   public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
       db.execSQL("DROP TABLE IF EXISTS "+ FRA_TABLE_NAME);
       db.execSQL("DROP TABLE IF EXISTS "+ ING_TABLE_NAME);
       onCreate(db);
   }
}

Thanks for the help.