I had the same issue this is the fix. purchase button, & delete & restart download
This solved my question Solvedby tedster998 on Apr 12, 2015 3:53 PM
I now have iPhoto 9.6.1 installed, but I first had to upgrade to Yosemite.
Here's my history when trying with Mavericks: I wasn't able to update from iPhoto 9.5.1 while running Mavericks - as I mentioned in my first post, I would get an error message when I tried to update iPhoto in Mavericks. When I deleted the iPhoto app from my Mac still running Mavericks, and went to the App Store "Purchased" tab and clicked "Install" next to iPhoto, it would install the old version 9.5.1 in Mavericks.
I'll walk through the steps I took to successfully install iPhoto 9.6.1 - steps 2 & 3 were dead ends, but I chose to mention them here in case others take the same path perhaps they won't feel defeated.
1. Upgrade from Mavericks to Yosemite.
2. After I upgraded my Mac to Yosemite, I started iPhoto but it told me that this version (9.5.1) isn't compatible with Yosemite (which I expected). It did give me the option to search the App Store for a compatible version, so I clicked on search and it told me the app isn't available in the U.S. app store.
3. Still running Yosemite, I went to the App Store "Purchased" tab and clicked the iPhoto "Update" button - but the update button had no effect and nothing happened.
4. Still running Yosemite, I deleted the iPhoto app from my Mac by moving it to the trash can and then I restarted my Mac. (I only removed the iPhoto app - I didn't remove or touch my photo library!) After my Mac restarted, I returned to the App Store "Purchased" tab and next to iPhoto was an "Install" button. I clicked Install and iPhoto successfully downloaded and installed 9.6.1. iPhoto is now working fine under Yosemite. iPhoto opened my photo library and all of my pictures are there. Everything looks normal.
Thanks everyone for your helpful suggestions!