You can right click on it and click on "Save As" to save it to your computer, then open it with whatever program you use to look at pictures. Then click on "View" and change the size. You should be able to just change the percentage from 100% to whatever you want, to make it bigger. But there are still only so many pixels there, so as you enlarge it, the quality's going to suffer. Only way to get a real good look would be to contact the person for the original. Hope this helps.

BTW I tried this on your avatar, and the results were SCARY