I've filed my 2019 return and my circumstances have changes so I want to redo my 2020 estimated taxes. Can't figure out how to do it. Please advise.

[Critter-3]

Since you used the online program this will not be as easy as if you used the downloaded version  ... now if the estimates you set up were to cover at least the prior year tax liability then you don't need to send in more if you don't want to ... you will not have a penalty.   If you simply want to increase the amount you send in for the January payment you can do that if you like.  

If you want to use the program then wait until the 2020 online system opens up in December  then log in and use the amendment process to open the 2019 return you filed and review the estimated payment section to make changes.    

https://ttlc.intuit.com/replies/4242911

[VolvoGirl]

If you know the amounts you want to send in just pay directly on the IRS website.  Or you can cross out the amount and enter a new amount or fill out a new 1040ES.

Here are the 1040ES instructions and blank forms (where to mail is on page 4)
http://www.irs.gov/pub/irs-pdf/f1040es.pdf

Or you can pay on the IRS website. Be sure to pick 2020 1040ES payment
https://www.irs.gov/Payments