The image that you see in the menu at the top is handled by the Globally Recognised Avatar, Gravatar. Your Gravatar is an image that follows you from site to site appearing beside your name when you do things like comment or post on a blog.
You can update yours or set it up on their site.
It is not necessary to change your profile picture from the default unless you wanted to. It’s more important to change the one in the Forums, as that is what everyone else will see.
The profile picture in the Forums is different to this one and can be changed there using this tutorial.