I filed my federal electronically and said I would mail what I owe but have changed my mind. I want to pay online.

Yes, you can pay your taxes electronically, but

• If you've filed the return you can not change it in the return
• You can make payments through a IRS Online account for individuals

@lisamorris1964 

Yep...you just use the IRS's DirectPay website.

https://www.irs.gov/payments/direct-pay-with-bank-account