I see older iMac's that have 20 inch screens for cheap, with almost no memory and small hard drives. Are these older machines upgradeable to Yosemite? Can I bring them up to 8 or 16 gb of ram? In other words, is it possible to modernize them? I just purchased a new 2014 Mid Mac Mini for my wife and am having a great time with my personal login on her machine, but she uses it a lot and I'm getting the itch. Any thoughts at all please.