Hi!
Usually Walt Disney World offers travel deals a few months in advance of travel dates. For your October dates, I would be keeping an eye on the
Special Offers page of DisneyWorld.com starting in early May. Historically, this is when deals for Sept and parts of October start to be offered.
Disney is also very good about applying newly released discounts to existing reservations. Typically all you will need to do is to call 407-W-DISNEY or contact your travel agent, and let them know that you'd like to take advantage of the discount.
Occasionally, if the resort or room type you've chosen is not available, you can opt to change resorts or room type in order to take advantage of the deal. Most times there isn't any charge to do so - but that will depend on when you call and which type of reservation you've made. The Disney reservationists are really great about this and will walk you through the process with no problem at all!
Hope this helps! Have a great trip!