I have a one year old Mac Air that says it using OS X 10.8.5. I get occasional prompts asking me if I want to upgrade to something called Yosemite. I'm a non-techie, and someone who hates change. So I've ignored it so far, not wanting to have things look different or act different in any way than than the way I'm used to. Is this fine, or should I bite the bullet and upgrade? What might I like or not like about it if I do?