Change Main Icons failed

Hi from Germany,

I worked for a long time with the 4.x.x Calibre version and - among other modifications - I changed some of the icons of the main toolbar individually (not by "change icon theme") - it worked perfect. The new icons have been placed within the folder

C:/program files/calibre2/app/resources/images and
C:/User/appdata/roaming/calibre/plugins (within the zip-files)

I now changed to the latest calibre program version 6.6.1, nearly all modifications still work - except most of the icons which are at the C:/program files directory (though I changed them [overwrite], just the icons within the zip-files are "up-to-date" ("count pages", "modify epub" etc)

Is there another location I oversee or what may be the solution?

Thanks in advance,
regards Peter

https://www.haselau.eu/media/cal01.jpg