How do I get iphoto to upgrade photo library after upgrading os from snowleopard to yosemite?

Go to the App Store, locate iPhoto 9.6, download and install.

To add to OT's advice:

You may need to delete your current iPhoto from the Applications folder, if it is a version of iPhoto '11, before the App Store will allow you to download it from the main page.

To locate iPhoto at the AppStore, open the "Featured" tab and enter "iPhoto" into the search field.

I just upgraded to Yosemite and now need to upgrade iPhoto, but I am scared to death that I'm going to lose my pictures. Can anyone give me any reassurance about this? I've read a few alarming reviews.

Make a back up first. Of course you should have made a back up before upgrading the system, you did, didn't you?

Sure - if you have a good, current backup then you are never at risk of losing you pictures - if you do not have a good, current backup then you are 100% guaranteed to lose them sooner or later - could be right now - could be during an upgrade or update - could be years from now but it will happen

And of course you actually have "lost" your pictures for now since you can not access them until you upgrade iphoto so even thought there are there on disk they are unavailable and essentially lost for now

So backup and install iPhoto 9.6

LN