1. Find a favicon. You can find some here.
2. Get its ‘direct link' (it should end in .gif or .png)
for example: http://media.tumblr.com/tumblr_lkl5gvCcRY1qfamg6.gif
-You can get the direct link by right clicking the favicon you want, then pressing ‘open image in new tab’. Then copy the url in that tab.
3. Find this code in your HTML theme code
4. Replace the word “Favicon” with your direct url.