When you plug your phone into your computer and open iTunes, you should be able to upload all or selected pictures into iPhoto. Once it is done uploading, it should give you the option to keep or delete the uploaded photos off of your iPhone.
Click the "Photos" icon on your iPhone's home screen. The Photos icon has a yellow flower on it.
Click your Camera Roll to view its contents.
Click the "Share" button in the top corner of your iPhone's screen. The Share button looks like a rectangle with an arrow pointing out of it.
Tap the thumbnail image for each of the photos you want to delete.
Tap the "Delete" button to remove all of the selected photos from your iPhone's Camera Roll.