How to Edit a row in the datatable

You can find that row with

DataRow row = table.Select("Product_id=2").FirstOrDefault();

and update it

row["Product_name"] = "cde";

First you need to find a row with id == 2 then change the name so:

foreach(DataRow dr in table.Rows) // search whole table
{
    if(dr["Product_id"] == 2) // if id==2
    {
        dr["Product_name"] = "cde"; //change the name
        //break; break or not depending on you
    }
}

You could also try these solutions:

table.Rows[1]["Product_name"] = "cde" // not recommended as it selects 2nd row as I know that it has id 2

Or:

DataRow dr = table.Select("Product_id=2").FirstOrDefault(); // finds all rows with id==2 and selects first or null if haven't found any
if(dr != null)
{
    dr["Product_name"] = "cde"; //changes the Product_name
}