I have recently set up a contract with a freelancer, but I accidentally set the whole amount agreed upon to one milestone. How do I change this so that the dollar amount is split up over several milestones?
Unfortunately, it's not possible to edit milestones that's been funded. However, you will be able to edit the amount when releasing the first milestone. After you release a partial amount for the first milestone, you can use the remaining funds in Escrow to fund the next one and so on.
I hope it helps.
It sounds like you're referring to Milestones which have been created for future tasks on an existing contract? Once a client creates a Milestone you as a freelancer can't edit it, regardless of its Escrow status.
At this moment you can continue with your freelancer and release less than what is funded. On the pre-established milestone, when you click the green "Pay Now" button, you'll be presented with the option of releasing a smaller amount and leaving the rest of the funds in escrow. After this, you can request a refund for the remaining funds. If you have any additional questions let me know. Thank you.