Hi Cidney, welcome to planDisney!
If you purchase theme park tickets without a Walt Disney World vacation package, there is currently no payment option available. The full amount is due at the time of the purchase. However, if you instead purchase a
Walt Disney World vacation package, you can make payments on your schedule up until the final balance is due 30 days before check-in (subject to change). You can make payments by signing in to your My Disney Experience Account online, hovering over the My Disney Experience link on the header, and scrolling down to "My Plans." From there, scroll down to find your resort reservation and click the "Make Payment" link.
If you prefer to purchase only theme park tickets, another option you might want to consider is purchasing Disney Gift Cards at your convenience from retailers that offer them at a discount. You can consolidate them up to $1,000 (subject to change) at the
Disney Gift Cards website and when you have enough accumulated to purchase the theme park tickets, you can do so using your Disney Gift Card(s). I use Disney Gift Cards for almost everything related to Disney to get the extra cost savings.
I hope you find this information helpful. Please let us know if there is anything further we can assist you with.
Diane