I can't manage to get gnome tweak tool to allow me to switch themes, nor to install the required extensions and have them working. Could anyone please give me any pointers?
EDIT: Fixed it, but I forgot how I did it. Sorry.
I had to face this problem again, and found a solution:
Istall the user-theme extension from ppa:
Restart by logging out and back in or with
Open the gnome tweak tool, go to Shell Extensions, enable the User Themes Extension.
Close the tweak tool restart gnome-shell again.
Now open the gnome tweak tool again and, under theme, you should be able to select your shell theme.