I need to empty my iphoto files as there is too much memory being taken up.
No, iPhoto files take up disk space, not memory. So if you think you're going to save memory be getting rid of them, you need to reconsider that idea.
You can move your entire iPhoto Library to an external drive and import new photos into it on that drive, so if that's what you want to do, these are the steps:
1. Format the external drive as Mac OS Extended (Journaled)
2. Quit iPhoto
3. Copy the iPhoto Library from your Pictures Folder to the External Disk.
4. Hold down the option key while launching iPhoto. From the menu select 'Choose Library' and navigate to the new location. From that point on itl be the default location of your library.
5. Test the new library destination and when you're sure everything is as it should be, delete it on your Macintosh HD.