Since Apple has removed iPhoto from the Mac App Store, the iPhoto Library Upgrader tool is really the only option to prepare your library given how many versions behind it is.
I want to verify you are downloading the Upgrade from the following page:
You should be receiving a disk image file labeled "iPhotoLibraryUpgrader.dmg"
Upon opening this DMG you should see an installer package labeled "iPhoto Library Upgrader.pkg"
If you run it you should have an application called "iPhoto Library Upgrader.app" in your Applications/Utilities folder.
If indeed you've run the installer and it reports it is successful then it should be there. However, if you're not seeing it then perhaps the Finder is not updating the file system view properly.
If so, boot into Safe Boot mode and see if you see the upgrader.
Restart your Mac
As soon as you hear the Startup chime, press and hold the SHIFT key
Continue to hold the Shift key until you see the Apple logo and progress indicator.
Then, let go of the Shift key and let it boot to the Desktop (it may take longer than usual so please be patient).
When at the desktop;
In the Finder, click the Go item in the menu bar at the top of the screen and choose Utilities.
Locate it and run the "iPhoto Library Upgrader.app" to perform the update.
When it has finished, restart your Mac and allow it to boot normally.
The next time you run the new Photos app it should properly import the iPhoto Library to it's own database.
I hope this helps, and if you have any further questions please let me know.