If you need the points in the first reservation, i.e., you would otherwise have to borrow points to make the new reservation without cancelling the first, then you do need to cancel the first reservation before completing the second on line. To cancel the first, you need to go to portion of the site that lists your existing reservations. Particularly during very high demand times, which includes the time you are trying to get near Columbus Day weekend, you can face a serious risk doing the change on line because between the time you cancel your first reservation and then try to lock-in the second reservation, you can lose both reservations to someone else and end up with nothing. To avoid that risk you can either wait to call at 9 or follow a procedure that supersnoop, a member of these boards, first published. That procedure requires that you would need to borrow points to make the new reservation if you did not cancel the first, and it goes like this:
1. You should use two computers, such as a desktop and an iPad. This may work with one computer using two different browsers but I have not seen confirmation of that yet.
2. On one computer, go to your existing reservation and get to the page where it can be canceled. Do not cancel yet.
3. On the second computer, start making your new reservation, and if it is available get to the first lock-in page where it says you have 20 minutes to complete the reservation and provides your contract or contracts where you are supposed to choose points. Those will show only your unused points when you get there.
4. Choose the contract or contracts you will use for the new reservation. The Borrow icon should come to life near the bottom of the page. Click on that borrow points icon. A window will come up that allows you to borrow or "cancel" the window. Now do nothing.
5. Go back to the other computer and cancel your prior reservation. Do nothing other than complete the cancellation process.
6. Now go back to the computer where you are making your new reservation. Hit "cancel" in that borrow window. It will disappear and your contract points will refresh and all of the points from the prior reservation will appear as available in your contract and then you can continue on with the new reservation.