change $WP_query

Hi,

i’m doing hard modifications to a wordpress, and i need to modify the query what use to show the post (i need to do this query twice with deferents values, why i modify the table of the database(i need to call the method the_post(); twice with deferents values in the query what use),

any can tell me where is the query to change it or how i can change for a new one?

Regards,
Shadow.