On joining you are given a random avatar, an image that is assigned to you and often used with or instead of your user name.
You can change your avatar to an image of your choice by uploading an image file or picture from your desktop. To do this, go to ‘My Picture’ under ‘My Profile’, and tick on custom, then browse to go to the picture/image you wish to upload from your desktop.
To change your avatar, upload another image under the custom section of ‘My Picture’, as above. Sometimes it may be necessary to clear the cache of your computer to change the avatar.