Create a Bootable External Drive
What I recommend people do when wanting to update is create a bootable backup. What this does is create an external drive you can boot off and test and install new things to your heart's content without touching your main drive.
A bootable external drives are great in case your system drive fail. You can boot off the external and keep working until you can fix the system drive. Or you can use another computer while yours is fixed. This has saved me many times in the past. :)
In essence, you create a clone of your current system drive and boot off it instead of your current internal system drive. What this allows you to do is test any update you may have without touching your main system drive.
This is also great to have in case you ever have a system drive failure you could boot off it and keep working until the system drive is repaired.
** Please make sure to make a backup of the Event folder you work on in case you need to open it in a prior version of Final Cut Pro.
Here is more information on how to create a bootable disk drive: https://discussions.apple.com/docs/DOC-6101
I use ChronoSync to make my boot drives, but there are others as well.