If you've gone through the process of uploading your avatar/picture in your Forum Profile Information, and it's not showing up, this is normal.
To fix the problem, hit ctrl + F5 on your keyboard. This will refresh your cache.
When you load a page, your browser will save files on that page to your hard disk. Included in these files are images. Instead of loading the files from the website again, it will load it from your hard disk. The reason you can't see your avatar change after uploading it is because your browser is loading your previously cached avatar, instead of your new one. By refreshing your cache, you'll be getting updated images.
If for whatever reason ctrl + F5 doesn't work, Google how to delete cache for your browser.