Ed,
When you install any version of Revit on your computer, it finds the 'old' versions and gives you the opportunity to remove them. In the case of a new Build, you simply install, and it will find and default to remove the old Build for you.
As for keeping everything, you can and should. There's an option about two screens into the install process that allow you to not re-download the content. Which, since you've already got the content, will save you a bunch of time.
It should also find your license and open up without re-authorization needed.
All your paths are saved to revit.ini & the shortcuts are in keyboardshortcuts.txt in the Program folder. If you save your Revit.ini & Keyboardshortcuts.txt file out to some other location prior to install, and then copy them back in (overwriting the default ones) Revit will even wake back up with all your pathing and shortcuts intact...
If you're rolling the new build out to an office, there's an option to make a Network Install Package within the install process. You set up a location for the .MSI package (I set it to the same location as the last one, just overwriting it), select not to download new content, set up your paths to the server and such, and then when it's done making the install package you simply send or tell everyone to click on the Installer Shortcut (or push it out via a login script or something) and it will automatically put the new Build on their machine, removing the old one, and set all the paths and such while it's at it. I did this today, for we just moved servers, and had to reset all the paths for Revit...