Extrafanart issues

I have noticed that Kodi (on my RPi2 LibreELEC setup) has created a folder named extrafanart in most of the folders with movies or TV shows on my Zyxel NAS, as it should have. But, I'm unable to delete those folders now as it requires "permission from Unix User\root to make changes to this file".

My google powers are weak and I haven't found a solution. Does anyone have any advice?