Ubuntu is one of the most user-friendly Linux distributions in the world. However, Linux distributions change a lot on every new release. Although we can upgrade to the newer release easily on Ubuntu, I suggest to have a fresh install on every new release.
In my opinion, it is a good practice to format your hard drive at least in four partitions. Such as
/boot (about 1GB)
/ (not less than 8GB)
/home (depends on your hard drive space reminded)
/swap (twice as your amount of RAM)
In this way, you can install and format /boot and / partitions and leave /home untouch on every new or re-install. All your settings at /home are reminded unchange as well as the data in that partition. Be keep in mind that you are NOT required to format /home partition.
You are also required to backup /etc/passwd and /etc/shadow when necessary if you have more than one user.
That's all. See you!
