Danny,
Go to MY HOME and then navigate to Main Configuration near the bottom of the page. Click on the edit by Personal information, email, password, etc.
There, near the bottom again will be the area to post the URL to your new photo. Make sure it is posted somewhere for you to link to. Such as, post the new one in the Signatures post and then link to that. You can't just try to include a "photo file" when you make the change. TBN needs to know where to go fetch it.
edit........
These photos need to be less than 5KB and around 80X80 pixels