How to upgrade to chrome 64 bit?
Chrome is updated automatically by a process that runs in the background. Though sometimes I have to launch it and update it from the"About Chrome" menu selection, that may me being to picky avoid what Little Snitch tells me about...

Anyway you don't (or shouldn't) have to do anything, it will update all by itself with no loss of anything. Just check "About Chrome" in the Chrome menu.