Hi I'm upgrading from aperture 2 to aperture 3 via the app store
before burning your Aperture 2 bridges, I'd take some precautions, if you have not done so already, to make sure the upgrade will be smooth.
You should be aware, that the upgrade from Aperture 2 to Aperture 3 will have to upgrade your library and afterwards you will no longer be able to open the library in Aperture 2. Some plug-ins may no longer work.
Just in case the upgrade of the will not work at the first try, make a backup of your Aperture 2 library and keep a working copy of Aperture 2. You can simply rename the application to "Aperture 2". This way you will be able to open your backed up Aperture 2 library, if need be.
The upgrade of the Aperture 2 library to Aperture 3 will be easier, if your Aperture 2 library has no problems and does not need any repairs. Apple recommends to run the Aperture Library First Aid tools to (repair and) rebuild the library in Aperture 2, before you first open it in Aperture 3 to upgrade the library. This rebuild may take a long time for a large library. To rebuild, launch Aperture with the key combination ⌥⌘ held down.
when I install aperture 3 will I have to transfer my pictures to a new library or will it use the existing one.
Once Aperture 3 is installed, you upgrade your Aperture 2 library by double clicking it, whereever it may be installed.
I have my aperture library on an external hard drive
Check the formatting of the external drive. Aperture 3 needs the drive to be formatted "MacOS X Extended (Journaled)". If your drive should be formatted differently, copy your library to a drive with the correct formatting.
Once aperture 3 is installed will i then have to remove aperture 2 from my computer
You can keep both programs, but rename the older Aperture version, so that it will not be overwritten by the installation of Aperture 3.
Regards and god luck!
Have a look at this support article: Aperture 3: Tips on upgrading an Aperture 2 library to Aperture 3
and also: http://support.apple.com/kb/TS2518 - scroll all the way down to
Additional Information - A note on upgrading your Aperture library