I have a USB Device (32 GiB) that i put an installer on and got openSUSE Tumbleweed with. I was wondering if it is still usable to change versions from a GNOME thing to a KDE Plasma thing. If someone could make a step-by-step guide to change from GNOME to KDE, that would be great, because i have NO idea how to work this on Linux.
Just use Yast Software Management.
Choose the “Patterns” view.
Select the KDE patterns. Checking my Tumbleweed system, that’s the “KDE Plasma 5 Desktop Environment” pattern. (You do not need the development patterns).
Install that and you are almost set. You will now have both Gnome and KDE installed. You can choose which you want on the login screen.
You are probably using GDM for login. On the screen asking for password, there’s a gear near “Sign In”. Click that gear to choose which desktop you want.
As an extra, install “plasma5-session-wayland” (it might already be installed as part of the KDE pattern)". That will allow use of KDE over Wayland.
If you wish, you can switch to SDDM for the login screen. Personally, I prefer GDM. To switch, use:
update-alternatives --config default-displaymanager
(run that as root).
I got into Yast software management but couldn’t find patterns. I am using Tumbleweed GNOME if that helps
I solved it myself.
You reboot your computer using the button in the top right,
Then hit C to open the command line when you select to boot regularly or in another mode
Type exit
Click Upgrade or Installation (i only did it on Upgrade)
You can select it from one of the menus that come up
I guess you just have to know where to look 
Yast Software Management: There is a row of tabs across the top. The left tab says “View”. Click on that for a drop-down list of views. One of those is “Patterns”.
After you have done that once, “Patterns” will show up as an additional tab in that row of tabs.
Okay, you solved the problem a different way. But you might as well give this a try so that you will know where to look.
On Wed, 23 May 2018 12:16:03 +0000, PandaR wrote:
> I solved it myself.
>
> You reboot your computer using the button in the top right,
>
> Then hit C to open the command line when you select to boot regularly or
> in another mode
>
> Type exit
>
> Click Upgrade or Installation (i only did it on Upgrade)
>
> You can select it from one of the menus that come up
That’s really overkill for what you’re trying to do - you don’t need to
boot from installation media and run an upgrade - you’re not actually
changing the operating system itself, just the desktop environment. 
–
Jim Henderson
openSUSE Forums Administrator
Forum Use Terms & Conditions at http://tinyurl.com/openSUSE-T-C
I now am beginning to understand why the title of this thread is so strange. It does not cover the subject at all.
But it seems that the OP has a huge misunderstanding as you point out.
@PandaR.
I hope you are still watching this thread after you have found a solution for your problem because we think you have some misunderstanding. In Unix/Linux, a desktop is just a bunch of applications, not an OS, nor part of it. Many installations even don’t have any desktop installed (so called Text Only systems). You may now understand the advices above, where you are told to just install the bunches of applications that belong to the desktop(s) you want to have (and those bunches are nicely bundled in Patterns for ease of installation).
And as Unix/Linux is a multi user, multi session system, different users can use different desktops of their choice either after each other or at the same time. An individual user can also choose a different desktop at each login.
I hope you now get the idea.