Hello MaTax91, and welcome to Seven Forums.
Actually you would need a 256x256 pixel ICO file to use. If you like, you could ZIP your PNG and upload
the ZIP in a reply post here. Afterwards, I would be happy to convert it into a 256x256 ICO file for you, and post it back in a ZIP. You could then use the tutorial below with step 5 to use the ICO file. Libraries Icons - Change
Hope this help,