COOCKIES

HOW CAN I UPDATE THE COOKIE VALUE FROM ONE PAGE TO ANOTHER.. I MEAN FOR AN INSTANCE, CONSIDER THAT I HAVE A USERID AND PASSWORD IN A PAGE, WHEN I REDIRECT THE PAGE, I SHOULD ACCESS THIS COOKIE AND SET THE VALUE FOR USER ID. WHEN I AM DOING LIKE THIS IT SHOULD REFLECT TO ALL PLACES(PAGES), WHEN I GO TO ANOTHER PAGE AND RETRIEVE THE VALUE IT SHOULD BE THE UPDATED VALUE. PLEASE ANSWER FOR THIS ASAP..
THAKS IN ADVANCE