It's complicated! From the IRS site, I learned about the EFTPS payment system, which, however, Turbo Tax does not use when paying taxes through Turbo Tax. Getting verified and access to that site takes about one week including receiving a PIN and access code! When on the EFTPS site, an agent there (via phone) is able to access your scheduled payment through the IRS site and cancel that payment for you. After the Turbo Tax originally scheduled payment is cancelled, you may then schedule a payment on the EFTPS site. You cannot automatically cancel the original scheduled payment yourself on the EFTPS site because that vehicle is not used by Turbo Tax. I don't know which pay system Turbo Tax uses, or why they cannot arrange a change-date through their system.
