To use your own custom favicon, you’ll have to acquire the Custom Design premium feature in the Upgrades section of your blog’s dashboard.

Once your purchase this upgrade, head over to the favicon upload menu which is available under Appearance > Favicon in your blog’s dashboard.

custom-favicon

Then, use the upload buttons to upload your favicon and reload your blog/site to see the changes.

The recommended size for this image is 128px x 128px, but you can also upload one icon for iPad, iPhone, or iPod Touch with 114px x 114px.
Accepted image types are PNG, JPG, GIF, and ICO, but we recommend that you upload the image in the PNG format. All images will be converted to ICO, resized, and compressed as needed.