iMac mid 2011 2.5Ghz Intel Core i5 Installed extra RAM to 12GB 133 MHz DDR3 Operating on OS X Lion 10.7.5 Mainly used for browsing, currently Safari 6.1.6 Have avoided upgrading OS or Safari because have experienced few problems to date and am not that savvy. Should I upgrade to El Capitan? And anything else I need to know!? I would appreciate any advice. And I really mean that.