Hi Daisy, welcome to planDisney!
Thanks for bringing your question to us, I'm happy to help!
Generally, we recommend Guests cancel their existing reservations up to 24 hours before their arrival date. This will open up reservation spots for other Guests to book! However, that is a recommendation. Guests can technically cancel their reservations even on the day of their visit!
In regards to how far out you can book a reservation, reservations can typically be booked up to 120 days in advance. So if you have a particular date in mind, make sure to book it on your calendar! Oh! And one more thing,
dining reservations can be booked up to 60 days in advance. The popular locations tend to book quickly, so I would definitely mark that on your calendar as a reminder to book right when your 60 day window opens!
Hope this helped!
See ya real soon!
Jin