You have to activate your 360 profile. To do that, go to your Yahoo! Answers profile, and then click on “Edit My Info”. If you haven’t created your avatar, at the top of the page, under “Nickname” is a line that says “Use my 360 nickname”. If you have not created your 360 profile, there will be a link next to it that says something like “Get my 360 profile now!” Click on it; it will be the easiest to use for the below.
Once you set up the profile, you can click on the button that reads "Edit Personal Photos". That takes you to a page, where you can upload an image you wish to use as your primary photo. Remember, it has to be in the JPG format, and it must be 5 MB or less. After you have added the image, you can set it as your primary. Then, go to your Yahoo! Answers profile, and then click the button that reads "Edit My Info". You will see three boxes down near the bottom toolbar on the page, and the middle one reads "Use my Yahoo! 360 Picture". Check the circle next to it, and then scroll down and save your profile. It will take a short period of time for the picture to process, so be patient.