To change the photo from your iPad or iPhone, open your profile.

At the bottom left of your image there is the symbol of a camera, click it.

Two options appear:

1) Take Photo: clicking this, you can take a photo and use it in your profile.
2) Choose Existing Photo: clicking this, you can use an already existing photo on your device and use it in your profile.

To enter or change a photo, you must have reached the 9th level of play.