Type W-2 into the search bar at the type of the screen. Click the jump link TurboTax provides. This is going to take you to the screen where your W-2(s) are / is listed. If there is an extra one there, you can choose delete to remove it.
If you are using the desktop version of TurboTax, the directions will be slightly different. Let me know in a comment if this is the case.