How do I upgrade iPhoto 9.2?

I recently upgraded to Lion 10.7.5 and now I find I need iPhoto upgrade to 9.2 to use photo stream. I don't think it came with my upgrade purchase because it would have upgraded automatically, right? How can I download the upgrade? I find working with App Store to be difficult. OS 10.7.5 is the highest I can go with my processor (Mac Pro 2x2.66 GHz Dual-Core Intel Xeon, 2 GHz DDR2 FB-DIMM. )

Thank you.

LGSmith