I think my wallpaper cache needs clearing. I am using 5.9.4 and I especially like the wallpaper of the day feature. However, the national geographic wallpaper hasn't changed in a week. I think the cache needs clearing. How do I do this? Thanks

Try to search for them:
$ command locate --regex "${HOME}.*/wallpapers" | less -S

A)
If You find Your current wallpaper's name:
(Make a copy of current wallpapers for case of emergency. )
Delete it and its not-wanted siblings manually. Maybe leave one single image there.
LogOff/LogON
Enjoy.

In case of problems:
Copy backups back.
LogOff/LogON.

B) If You don't find Your current wallpaper's name:
$ command locate --regex "${HOME}.*<whatever-You-think-fit-to-be -searched-for>" | less -S

louparker wrote:... using 5.9.4 and I especially like the wallpaper of the day feature. However, the national geographic wallpaper hasn't changed in a week....

Bug 379003 - Wallpaper "Picture of the Day" from National Geographics only changing after reboot or not at all - https://bugs.kde.org/show_bug.cgi?id=379003