If you are using TurboTax online, click on the Deductions Tab.  Check the box beside the First Time Home Buyers amount.  Click Continue until you get to the First Time Home Buyers Tax Credit.  Choose No from the drop down menu and remove the amount (5000) from the second box.

If you are using TurboTax download, choose Deductions and Credits from the left hand navigation bar.  Choose Payments Profile, then check the box beside First Time Home Buyers amount.  Click continue until you get to the First Time home buyers tax credit.  Remove the $5000 from the box on this page.

Be sure to leave the box checked in your profile showing you are entitled to the First time home buyers amount to make sure all of these pages show up for you to make the correction.