C# - Remove row from database, and update it with new information, using data adapter

Question

I have a database where I store my current stock portfolio (aka Positions), and i want it to update every time i buy.

Database contains columns: 1. Id, 2. Ticker, 3. Shares, 4. ProfitLoss, 5. TradePrice, 6. CurrentPrice, and 7. TotalValue

So basically I click BUY, then it inserts a new row. If I click BUY again, it won't delete the row, and thus won't update it with the new one because the index primary Id still exists.

And this is the error I get:

An unhandled exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll

Additional information: Violation of PRIMARY KEY constraint 'PK__tmp_ms_x__3214EC072159A622'. Cannot insert duplicate key in object 'dbo.Table'. The duplicate key value is (0).

The statement has been terminated.

What am I doing wrong? Stuck on this for a good couple of hours. Thanks, Here's my code below:

// create Positions database
PositionDBDataSetTableAdapters.TableTableAdapter Position_table_adaptor = new PositionDBDataSetTableAdapters.TableTableAdapter();

private void btnBuyToOpen_Click(object sender, EventArgs e)
    {
        // declare variables
        int shares = (int)nudShares.Value;
        decimal commission = 5;
        decimal cost = 0;
        string menuItem = menuSymbol.SelectedItem.ToString();

        // update buying power
        // and purchase and update Positions database
        if (menuItem == "JERO")
        {
            cost = (JERO.Price * shares) + commission;

            // If user has enough buying power,
            // update the buying power,
            // and update positions database.
            if (updateBuyingPower(cost))
            {
                if (Position_table_adaptor.GetData().Select("Ticker = 'JERO'").Length != 0)
                {
                    Position_table_adaptor.GetData().Rows.Find(0).Delete();
                    Position_table_adaptor.Insert(0, "JERO", shares, 0, JERO.Price, JERO.Price, cost - commission);
                }
                else
                {
                    Position_table_adaptor.Insert(0, "JERO", shares, 0, JERO.Price, JERO.Price, cost - commission);
                }
            }
        }
    }