Short guide on how to upload your avatar:
1. Go to your User Control Panel, then go to Edit Avatar (if you are having trouble finding that, just click on the link and it will automaticaly take you there)
2. Check the "Use Custom Avatar" box
3. Then you have two options; You can choose to upload an image which is stored on your device, or you can upload a remote file, all you need is a link.
4. Don't forget to hit the "Save Changes" button
* If your avatar could not be uploaded, make sure that it meets all requirements (the image must not be animated, it must be within the 68x68 pixel limit and its size must not exceed 19.5kB. *note that the image is automaticaly resized if you are uploading from your device)
The picture you are trying to set as an avatar probably doesn't meet the size requirements.