I am running OS 10.7.5 on a Mid 2010 Mac Mini with 8 GB 1067 MHz DDR3. My machine is slowing down recently. The finder windows will close for no apparent reason while I am using it. I am wondering if I should upgrade the OS. I have been a Mac User for 20+ years. Every single time I have upgraded OS I have lost some functionality/access to a program that I use. So, I have been very slow to upgrade. Will my Mac be more stable if I upgrade? If so, Mavericks, Yosemite, or El Capitan? Thanks.