Go to your "User Control Panel" at the top of this forum
Select "Edit Profile" (which I believe is the default tab)
Find the "Avatar / Profile Photo" section of the "Edit Profile" tab
In the "Edit Avatar" box - make sure "Upload a file" is selected and click on the 'Upload a file" text (that text is actually a link)
Use the file selection dialog to find a profile picture and upload it. There are some limits on the size of the photo - mine is 640x480 PNG 218 KB
Also make sure, after you upload the file, that "use your avatar as profile photo"