When I tried to open iPhoto, it says that I needed to update to the latest version.
Im using OS X Yosemite system.
When I search on App Store it says that "The item you've requested is not currently available".
iPhoto and Aperture are not supported any more and have been removed from the app store.
From wikipedia (here):
On April 8, 2015, Apple released OS X Yosemite 10.10.3, which includes the new Photos app. iPhoto and Aperture were discontinued and removed from the Mac App Store.
The successor app Photos was just released – on the corresponding page at apple.com you'll find further information about this release.
I just went through this with a friend of mine. We found and installed iPhoto from the App Store under Purchases.
1) Launch the terminal (don't be afraid, type "terminal" on spotlight or in /Application/Utilities/Terminal(.app)
2) type : /Applications/iPhoto.app/Contents/MacOS/iPhoto