first you'll need to make a yahoo 360 account:
http://360.yahoo.com/login.html?.done=http://360.yahoo.com/
after clicking "getting started" and creating a page, click "edit personal photos"
click "browse" and select the picture you want (it must be saved to your computer) and press "save" at the bottom of the page.
go back to "edit personal photos" and select the "set as primary" bubble next to your picture and press "save" again.
the picture you want should now be shown on your 360 page.
after all this, go back to yahoo answers:
1. go to "my profile"
2. click "edit my info" in the top green box
3. select "use my yahoo! 360 picture"
4. click "preview"
5. click "ok"
hope this helps. good luck!!