I have Ubuntu GNOME 16.04.2 but now I prefer to switch to Ubuntu 17.04 with plasma 5.9.
I downloaded the ISO file. I prefer to totally remove Ubuntu GNOME from the system and install Ubuntu 17.04, but I want to save my home partition.
Can I just delete root and swap partition and remake new ones for Ubuntu 17.04 at install time?
To accomplish changing Ubuntu GNOME into Kubuntu, you could upgrade to Ubuntu 17.04 then after the upgrade has gone through successfully, you can run some commands to install KDE then remove GNOME.
After you have upgraded to Ubuntu 17.04, you would need to install KDE first.
To install KDE, you would open up a terminal and type:
sudo apt-get install kubuntu-desktop
After you have done this, you should reboot and then at the login menu you would click the Ubuntu icon next to your username and change it to KDE/Kubuntu (I am unsure what the exact name of it is) as seen in this picture: 
After this, to remove GNOME, you would then open up a terminal and type:
sudo apt-get purge ubuntu-gnome-desktop
Alternatively, if you do not want to go through with doing all of this, you could back up your data (possibly to an external device) and then simply do a clean install of Kubuntu 17.04. I am a big fan of clean installs, and this is probably what I would do.
Best bet is to backup your home partition to your local computer or somewhere you can store it for a short time. Then do a clean install of 17. Another option would be to upgrade from your running machine using "sudo do-release-upgrade" then purge the old Gnome.
