There is nothing to transfer. iPhoto and Aperture share the same library format. You can simply open your iPhoto Library in Aperture, if you have the latest iPhoto version and use both programs on the same library.
See this support article: Aperture 3.3: Using a unified photo library with iPhoto and Aperture
You can also use Aperture to merge all your iPhoto Libraries into one, single library, see:
But even, if you will only use Aperture in future, I'd not delete iPhoto. You may find it useful to have occasionally, see Keep iPhoto - It May Come in Handy!