[Users] Change Claws-mail icon?

[altesCoon]

Hi again.

I'm just trying to change the program icon of claws mail (Win7-system).
I used the program "Ressource Hacker" and replaced all icons in the
exe-file. On the desktop and win-explorer all looks fine now. But when
i start claws mail, the program icon in the task bar and on the
program title bar is the old one.

Does anybody know, what i have to do? 
Does it have to do with gtk? 
What about the program "gtk-update-icon-cache.exe" under windows? 
Where is the old icon still on my disk? 

Regards
  altesCoon