//Put this in your DAO or Activity

public void alteraTarefa(yourclass yourclass){
ContentValues contentValues=new ContentValues();
contentValues.put("yourdbcolumn",yourclass.getyourvaluefromclass());
contentValues.put("yourdbcolumn",yourclass.getyourvaluefromclass());
contentValues.put("yourdbcolumn",yourclass.getyourvaluefromclass());
db.update("yourtable",contentValues,"your_column_name_to_do_the_where="+ yourclass.getyourvaluefromclass(),null); /*<------ NOTE: if you do the where with a string instead of int you have to do the where with the '' */ 
}