I have just updated my i mac to OS Yosemite and 4GB of memory but this is the report I get when I try to open the down load - Your computer’s video card does not meet the minimum system requirements.
iMac (20-inch Early 2008), OS X Yosemite (10.10.4), memory 4 GB
Then your Mac's GPU is too old, plain and simple. A 2008 Mac is going to start hitting a brick wall about now, and I'm going to bet you see more and more new/updated apps not run on it. 4GB is also not really enough to handle video editing, 8GB min real world, if not 16.
So, go to the Apple menu, to About This Mac, and post what graphics card you're Mac has installed.
Graphics card compatibility for Final Cut Pro X, Motion 5, and Compressor 4 - Apple Support
Downloading Final Cut Pro
