Your pictures are managed here (or via settings in the main menu).
You can scroll to an existing picture and change any of the details you want. Click 'update' on each picture after you've made the changes; (don't amend details on more than one pic at a time or only the pic you click 'update' on will get changed).
To upload a new picture, click ADD A NEW PICTURE at the top of the page (or scroll to the bottom).
Click the 'choose file' button and select the picture on your device.
Add a description to appear on the pic. This is optional, but can help people find your stuff.
Select whether you want the pic to be your main pic, a regular pic or a private pic, (you'll need to set a private content password first).
Select 'what's visible' for (ONLY) what appears in the pic; (i.e. don't click face if your face isn't in the pic). These labels are important.
Tick to confirm the picture is of yourself and click 'add'.
Wait a few seconds, especially on a slower connection, for the picture to upload.