Download and unzip this archive :
Replace the Diffuse texture with your own picture, in square format, 1024x1024 for example. Make sure the file is in .png and has exactly the same name
Upload the fbx as attachment on the neck, glasses or ear
If necessary use the new edit attachement feature in the lookbook to place the attachment in front of your avatar's head.
Save the look.
Now you can select this avatar's thumbnail as your profile picture for Sansar.