Whit a square image (PNG, JPG or GIF) in hand, open the site Favicon & App Icon Generator and upload your original image.
Click button Create Favicon and wait a moment for the website to generate the icons of various sizes automatically.
Download the generated package, unzip and delete the following two from the extracted files:
Now, copy the rest image files (
.ICO) to cover the original one in folder
Lastly, don’t forget to rebuild your site so that the icon becomes your custom edition.