Tina,

This depends on how you imported your photos from iPhoto to Aperture. Before deleting the iPhoto library, we want to be sure that the photos in Aperture aren’t in fact referencing the ones in the iPhoto library!

Assuming you have a totally independent Aperture library, then it’s safe to remove the iPhoto one. As Chris suggested you may want to archive it “just in case”, but as long as your Aperture library is backed up (check out Backblaze for cloud backup if you haven’t already), it’s probably not necessary.

If you ever need iPhoto features that aren’t in Aperture (such as making greeting cards and calendars), you can actually access your Aperture library from within iPhoto.