Click on "Federal" in the left navigation black bar.
Then on the top, click "Deductions & Credits"
You should see a table titled "Your tax breaks." In this table, you should have a "Traditional and Roth IRA Contributions" row. Click the "Edit" button.
You should then see a checklist of types of IRAs. Uncheck the one you don't want to include and click "Continue."
On the next page, you'll be asked to confirm to delete this contribution.
