In the Search box type "estimated taxes paid" (without the quotes) then click the link that says "Jump to estimated taxes paid." On the screen that says "Estimates and Other Income Taxes Paid" click the Update or Revisit button for "Federal estimated taxes." It will then show the amount that you entered, and you can delete it.

May I ask why you entered it there?  Did you actually send in any estimated payments during the year?  It might help us understand what users are doing when we answer questions.  Sometimes people ask why the tax due went to zero and this may help explain it.