create a stored procedure if it doesnt exist using a ddl in db2
IBM Added The OR REPLACE option in version 7.1

So your code should work like this :

CREATE OR REPLACE PROCEDURE ITIMUSER.GIAM_PRIVILEGE_MIGRATION()
SPECIFIC ITIMUSER.GIAM_PRIVILEGE_MIGRATION
LANGUAGE SQL 
BEGIN 

......
......
update/select statements
......

END