To change your message board profile photo (avatar), start by logging into your account here.
Next, visit the forum list. In the top right corner, select your current avatar (the circle in the top right hand corner as pictured below).
Selecting your avatar will display a menu of items. Hover over the circular icon to see the "edit" option. Click on edit.
This will bring up a screen that prompts you to upload your chosen avatar image as pictured below.
For best results, choose a jpg or png file that is at least 400x400 pixels. If the image is too large, you will be prompted to save the file as a smaller size. You can use a free online service such as Shutterstock to scale your image.