The opportunity to specify how much of your educational expenses you want to apply to trying for tax credits is under Deductions & Credits -> Education -> Expenses and Scholarships (Form 1098-T). Near the end of the inteview is a page entitled "Choosing a larger education credit or deduction." You can also get there from the page "Here's Your Education Summary" if you click Edit under "Education Information"
Things seem a little different now from when I went through, but this should help.
