how to use update() method instead of add() in SharePoint on Job Timer using visual studio c#

See more:

C#

Visual-Studio

VS2010

, +

Hi!, i have created a solution in SharePoint from visual studio C#. I want to create a Job Timer so i have created a c# class too. but now I'm adding a new row to task list
but what i want really to do is to update a specific row not to add new one. the code belongs as follow:

 public override void Execute(Guid targetInstanceId)
{
    SPWebApplication webApp = this.Parent as SPWebApplication;
        SPList taskList = webApp.Sites[0].RootWeb.Lists["Tasks"];
        SPListItem newTask = taskList.Items.Add();
        newTask["Title"] = "New Task" + DateTime.Now.ToString();
        newTask.Update();
}

I repeat again instead of add new row i want to update. Could anyone help me please.