STEP 1:
Click on your username located in the top right corner of the screen.

STEP 2:
Select "My Profile" from the menu.

STEP 3:
Click on the black "Edit My Profile" button.

STEP 4:
Click on the "Change my Photo..." Button.

STEP 5:
In the pop up window you have three settings to adjust (ignore the Gravatar section).
- You can either choose to Upload a picture by using the "Browse..." button.
- If you have found a file on the internet you can paste an address to that image here (e.g.http://www.example.com/picture.jpg)
- If there is a particular part of a larger image that you wish to use click on the "Adjust Crop" button and draw a box around the area you want and press "ok".

STEP 6:
Now you have added your image you can click the "Done" button to accept the changes or click the "Remove Photo" to return back to the default avatar.

Thats it! Enjoy your new avatar!