Set up a mirror test site and try upgrading there. Once you work out the kinks - then go live with it. Use Joomla Pack...then make a separate folder for installing back-up site. Then work there on upgrade.
Once you have upgrade running smoothly joomla pack it and replace current site...
Just make sure you put up a doing maintenance for site page up first while switching. Its a lot easier and is really fast. Then you can also test new features on the back up too before setting them up on the live one. ;D

thank you wingman