Or, just update the Yosemite install that you are now using.
I suggested making a clone, booting to that, so that you can update the clone, or do anything else with that clone. Your original stays untouched, on the internal drive. If that works out well for you, and those areas that you need to work, are working, then you can clone your clone, all updated and working, back to your internal drive.
Or, just make a clone on an external, leave the new clone untouched, and just update your internal drive. If things don't go well with the update, you can simply clone your complete drive back in place.
Clone is a complete, bootable copy. It would be on another drive, of course. It's really just a full backup of the drive, so you could use any method that you know leaves you with a (bootable) backup. Some users use Disk Utility to make a "restore" of your drive to another drive. Or, many users recommend dedicated apps, such as Carbon Copy Cloner, or SuperDuper!
This guy seems to prefer Carbon Copy Cloner, and I see it mentioned probably more often than other apps.
Use whatever you like to have a safety copy, so you can easily go back, if things go wrong with an update.