(Copied from this post: http://multiplynewbie.multiply.com/journal/item/6/Headshots)
There are two ways to change your avatar.
1. If you have just created a Multiply account and you still have the question mark headshot showing, there will be a link right over that headshot enabling you to add a new headshot. Just click on that link.
2. If you’ve uploaded a headshot and now you want to change it, click on “customize my site” in the right rail of your site. Now you’ll see a button around your current headshot that says “edit.” Click on it. This will take you to a page where you can either select an older headshot that you’ve uploaded, or you can upload a brand new headshot if you prefer.