I just updated it via the App Store, took an hour so including download, everything worked afterwards, then did another backup. It wasn't a painful process, not sure what issues you've read in the mixed reviews, seems to be ticking over nicely for me. Think I had this handy but it took care of itself.
http://www.macworld.com/article/2986158/operating-systems/how-to-install-os-x-el-capitan.html
PS - I didn't leap from Snow Leopard straight to El Capitan