First of all, backup all your personal data in your current home directory to an external medium (or somewhere convenient)
There might be better ways of doing this but this is what I can think of:
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Create a new user with admin right for your KDE
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Install EnOS list of packages for KDE:
eos-packagelist --install KDE-Desktop
- Enable the display manager:
sudo systemctl enable --force sddm
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Reboot and login to your new KDE user account.
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Remove Xfce
sudo pacman -Rs $(eos-packagelist XFCE4-Desktop)
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Remove your old user account.
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Look for probable leftover orphan packages:
pacman -Qqtd
and remove them if there are any. -
Copy back your personal data and decorate your new home.
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Enjoy!