Sorry for my english...

I've installed zen cart in my store succesfully but I need to edit many products at the same time.
For this, I use Data manager and import works great!. I need updated the catalog every day with information about stock and price, but I don't want to create all the products each.
I'm trying to edit the code for Data manager, and I think that questio is in import csv information to MySql.
I find this:
Code:
	if ($import_method == 'insert') {
					$import_csv_query = "INSERT INTO " . $current_table . ( $sql_fields !== false ? " ($sql_fields)" : '') . " VALUES ";
				}
And try to add a "ON DUPLICATE KEY UPDATE" instruccion, but always failed!
anybody can help me, please?