Right click on the image and save it (make sure you keep it as a .gif file) then go to your front page. Your icon at the top should show a pencil when you mouse over it. Click and you will be given the option to add a new icon. At the very top of your page, where it will say "Deviant ~MissKittyCat111", with a down arrow, will open a list that gives you the option to change your avatar (and signature where you can add credit to me) as well.
BAH. I redid my avatar, then I found out my Signature has too much crap on it that I can't get rid of. Would you mind me putting the credit on my profile instead? ~Won't use until answered for safety reasons. >w<