Which iPhoto version do you have? If your Aperture and iPhoto versions match, you can simply open your Aperture library in iPhoto. The library format is the same and no need to transfer anything.
In iPhoto 9.6 you would simply launch iPhoto, use the "File" menu. File > Switch to Library, then select your Aperture library from the library chooser panel and you are done.
See this support document: Aperture 3.3: Using a unified photo library with iPhoto and Aperture
There is no need to uninstall Aperture. It will not save much space, and even if you want to use iPhoto from now on, you can always open your iPhoto Library in Aperture, if you want to use an advanced editing option or need to repair links to missing original files or similar.