Hi Micah,

 Please refer below Code.

 Code

private void UpdateStock(string item, string qty)
{
    string constr = ConfigurationManager.ConnectionStrings["DB"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        string query = string.Empty;
        using (SqlCommand cmd = new SqlCommand())
        {
            if (Status.SelectedItem.Text == "Carton")
            {
                query = "UPDATE Store_Table SET Carton = Carton - @Qty WHERE Item = @Item AND Store=@Store ";
                cmd.Parameters.AddWithValue("@Item", item);
                cmd.Parameters.AddWithValue("@Qty", qty);
                cmd.Parameters.AddWithValue("@Store", Department.SelectedItem.Text);
            }

            if (Status.SelectedItem.Text == "Pocket")
            {
                query = "UPDATE Store_Table SET Pocket = Pocket - @Qty WHERE Item = @Item AND Store=@Store ";
                cmd.Parameters.AddWithValue("@Item", item);
                cmd.Parameters.AddWithValue("@Qty", qty);
                cmd.Parameters.AddWithValue("@Store", Department.SelectedItem.Text);
            }

            if (Status.SelectedItem.Text == "Roll")
            {
                query = "UPDATE Store_Table SET Roll = Roll - @Qty WHERE Item = @Item AND Store=@Store ";
                cmd.Parameters.AddWithValue("@Item", item);
                cmd.Parameters.AddWithValue("@Qty", qty);
                cmd.Parameters.AddWithValue("@Store", Department.SelectedItem.Text);
            }
            cmd.CommandText = query;
            cmd.Connection = con;                
            con.Open();
            cmd.ExecuteNonQuery();
            con.Close();
        }
    }
}