I have made a double entry on schedule D lines 1a and 1b. I see I should only have entered the data on one of the lines. How do I correct it?

Try this:

1.  Click Federal on the left-hand side menu.

2.  Click Income across the top.

3.  Scroll down to Investment Income and click Show more.

4.  Click Start or Revisit by Stocks, Mutual Funds, Bonds, Other.

Go into the entry that has the error to fix it.